I. THE CEROXOLOOT AND QEkEML XATURE OF THE BEHAVIOR O F

THE CHICK EMBRYO

ZIXG TANG X U 0 h'atiolal Crulrd Unioersity, 3-anWag, China

This is the first of n series of reports on the ontogenr of embryonic behavior in birds. We used eggs of hens, pigeons, nltd ducks as our material, but the present report deals solel?- wit11 the beharior of tlie cliick embryo.

TIIC purpose of the present report is to give, 1) a descrip- tion of the general method \rllich \re have de~ised for the direct mid continuous obsen-ation on the bird embqo and, 2) a chronological table and a general description of the nature of the behavior of the chick embvo to serre as a back- ground for the subsequent articles of this series.

A critical review of previous work on embq-onic and fetal behavior in vertebrates will be published elsewhere.

Xf ETHODS

Operation dereral montl~s 11ad hal spent without satisfactory resu1t.s

in an attempt to substitute an artificial transparent mem- brane for the opaque inner shell membrane of the hen's egg. r e were thus forced to abandon this method and our atten- tion mas then directed to the possibility of making the inner shell membrane transparent instead of removing it.

Failures to obtain satisfactory results ~ 6 t h various oils brought us to a realization that in order to secure satisfactory results we mnst use a material vhich possesses the following properties: 1) It mnst stick to the part of the membrane to

which the material is applied and not distribute itself over .

other regions. 2) I t must make the applied part transparent. 3) I t must protect the part from evaporation. 4) It must not cause any chemical change in the membrane which might affect the embryo and the material inside the membrane. We finally found that ase el in fulfilled satisfactorily the above requirements. The method may be described as fo1low.s:

The shell of the blunter end of the egg together with the outer shcll membrane attached to i t was cut with a pair of fiuc scissors as far as the inner shell membrane, nest to the air cell, leal-ing the whole inner membrane intact. Melted vaselin was immediately and rapidly applied with a Chinese writing brush to the part of the inner membrane facing the blunter end, care being taken that the temperature of the brush \ms not too high for the egg. The coating of raselin was extremely thin and when thus appiied on the membrane \s-ould remain in n semiliquid condition a t the temperature of the incubator, producilrg such a clear transparency that the embr?-o, tlie extra-embryonic circulation, extra-emb~onic membranes, and the yolk sac near the blunter end could be obser\-ed clearly. In fact, as far as c l e ~ n e s s of observation is concerned, the method of coating rasclin is just as g o d as tlie removal of the membrane.

Tlre opcrt~tion did not cause any undesirable effects on the e m b ~ o . In fact, operation and coating could be done on the first or second day of incubation and the embryo developed ~~ormnlly up to hatching, so that wc were able to make con- tinuous obscn-ations on the movemcnts of the same chick from the time of operation until hatching was completed.

Besides observations on embryonic movements this method also enabled us to study experimentally the causal factors \rhicll determine changes in embryonic positions from the beginning of incubation to hatching and the effects of mal- position on structural derelopment.

When the room temperature was lower than 80DF., the operation was performed in an incubator which had no eggs but whose temperature was maintained a t 103OF. After the

operation the egg was transferred to the 'observation' incu- ' bator, which will be described presently. The temperature of

the incubator varied betweon 103OF. and 104°F. I n this con- nection, mention must be made that frequent exposure of the operated egg to 10%- temperature usually had detrimental effects. Lf the room temperature Was lower than 70°F., and the operated egg was left uncovered and placed near the door of the incubator, frequent opening of the door was often suffi- cient to cause retardation of development, o r even death, of the embryo. This could be e a s i l ~ avoided by keeping the room temperature relatively high and especiall~ by covering tightly the operated end of the egg with a portion of an old eggshell, which also helped prevent excessive evaporation. During observation the cover was removed.

As incubation proceeded, the air cell increased in size day i?fter dzp, a=d tho area of the iiiiler shell membrane, nest to the air-cell end, was also proportionally increased; i t was necessary that from time to time more shell a t the blunter end be removed and the additional portion of the inner membrane be coated with ase el in.

Xo antiseptic measures were necessary because the shell membrane was not remored and because the coating of rase- lin generally prevented the entrance of micro-organisms.

Obseruation In most parts of this investigation three incubators were

used, 1) one for keeping, the eggs before operation, 2) the second, in which the operation was done, and, 3) the third, which was used for observation. The temperatures were practically the same for aU the three incnbators. The 'obse~~at ion ' chamber was a modification from a commercial incubator and was made to suit the purpose of observation by having glass on three sides. This enabled one to observe the movements of embryos of several rows of eggs placed near the glasses of the incubator. The egg tray in the 'obsema- tion' incubator was so partitioned as to keep the eggs from rolling about. Observation was always done by looking

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398 ZIRG YANQ XU0 EMBnYOlIC BEHATI08 A V E ~

r , In obsemin6 embryos of less than five daFs incubation Our general practice was to stand fie egg with

its operated end for several hours before the observation period, 80 that the embv-o mrould gradually turn to the trans- parent Part of the inner shell membrane. Sometimes it was

J,, order to ¶uantitativelr the movements of :..

c m ~ r ~ o s , 'ol,scn-atjon dial' was devised. This dial was

clru\,.l, a celloidin paper, graduated in millimeters, and :h d,,cd to w-l,icll --as made from na old egfFhel1. - :'. size of alld of each dial varied ~ ~ ~ o r d i l l g to the size ,:;

('oa,rot rsperi?~retlts a d critical fcsts

The eggs

., highly correlated with the size of the egg. AII the eggs laid by hens raised in the lnborntor~ and were collected manT

In 1 the total number and percentages of the first earance of each of the movements of the embvonic chjck arranged in chronologica~ order. It \~-i]l be lloted that the

situation.

. . - ., , . . _ _ _.,,. . *....-. . - --: ... . ' . . . . ' .- ' .&~

408 m a YI~PO KUO

of movements to hatching. In most of these chicks the

behavior after hatching was also obaemed for two days. In table 3 the averaged maximum frequency (hl.F.), the aver- aged madmum extent (ALE.) of each movement, and the num- ber of chicks are presented. I n the table frequency refers to the number of morements per minute, while the extent of morements is stated in terms of millimeters.

Heart beat

As the heart beat and its relations to the embryonic move- ments will be fully discussed in the sixth article of the series, we merely wish to point out here that the number of heart beats per minute a t any age is nearly twice that reported by prerious investigators, and is highly correlated with activi- ties of the embryo.

Head and body vibrating movemeats

These are passiw motions caused by heart movements and the circulating morements of the large blood vessels of the embqo. The morements are a t first v i e slight, visible only under a microscope, but in embryos older than three dsrs of incubation, they could be seen clearly without the aid of a microscope. They are slight jerking or vibrating motions of the head and the t d - identical in rhythm ~ i t h the pulse.

The vibrating movements of the head and of the bod? aTe to be distinguished from the lifting, bending, and turning ~norements of the head and the trunk. The latter movements are m ica1 physiological responses to stimulation, and might Ire properly called 'active' morements. The ribrating move- ments appear many hours earlier than the active movements of the head.

The head Tibration always appears earlier than the vibra- tion of the trunk. While the ribrations aare too slight to per- mit any quantitative measurements by our 'observation dial,' we have found that in*practi& every case the vibration of the head and of the region near the heart is most pronounfed.

EXBBYOETO BEaVIOB IX AVE6 409

As will. be seen by examining table 1, the earliest appear- ance of the vibrating movement of the head and of the trunk

. is between sixty-six and seventy-tsPo hours of incubation. But in most cases, head vibration appears between sixty-eight and seventy hou'rs, while trunk ribration appears mostIy between

.seventy and seventy-two hours. ' A s would be expected, the vibrating movement, especially

that of the head, is closely correlated with the cervical flexure. As the flexure becomes more complete and the beating of the heart gradually increases in strength and amplitude, the head vibrating movement also increases in magnitude. On the other hand, as the head and trunk become larger and heavier and the cervical flexure is being lost, and the head elevated and as tlie heart gradually retreats to the thoracic region, the vibratiug morements also gradually decrease in magni- tude and finally disappear. I n most eases, the vibrating movements disappear entirely after the s k t h day of incuba- tion, and in only a few cases, such movements are seen on the

Tlre passive vibrating movements of the head and of the t m ~ h are antecedent to the active movements of head lifting and bending and of jerking of the trunk, respectirely, which

, later is in turn antecedent to bending and extension and lat- eral turning of the trunk, although the passive vibrating morements do not disappear with the appearance of these active morements. During the fourth day of incubation, the magnitude of the head vibration ie so much increased that i t appears like continuous rhythmic nodding of the head corre- sponding to the rhythmic heart beating. Occasionally one of these nodding movements becomes so extensive that it turns into head lifting. This occurs about once in one or two min- utes. This is the actual origin of head .lifting that we have observed in a great many chick embryos. Such a lifting movement is really a physiological response of the head to .the heart beat in fact, I have found that before the contxac- tion of the d o n muscIe appears, the beating of the heart is almost always the necessary stimulus for head lifting: the

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410 ZING YANO xu0 411

and thereafter, head lifting disappean in most cases end had bminb. takes its place. (It must not&, though, that - in certain seven-da~ embvos passive head lifting is obaemed in ~onjnnction with the ertension of the tmnk. In no case . did we ever find active head lifting after the day.) But

' even if bead lifting per6iS.t~ after the .*h day in a few cases* it much slighter than the bead-turning movement

Head turaing As before, tile lat.ernl turning of the liead appears

later than head lifting and bending i t first appears ,55th head lifting as a mhed form of movement, but praduallp increases in the =tent of movement (table 2, colUIM 61, and finallr the major mOVernent of the head, Lend lifting eiWler disa~pears entirely or beeomes a minor moue- merit and subordinate to the turning movement. ~h~ lateral tumb the bead i n ~ 0 l ~ e s the whole neck besides the bead.

The f r q u e n c ~ of head turning increes greadl. btaeen the day and ninth day of incubation, but falls rapidll after the ninth (table 2, column 5). Tile extent of the movements varies from 1 to 6 mm. o f the 212 embrpos,

: Itsme hesd-turning movements on the fourth .day. me lIwber is increased to 147 on the fifth day. B~~~~~~ the and days all of the 212 perform

'. the day and tenth dag of incubatios the lies one of its sides in contact a i tb fie

*, has pointed oat, n.hen the lateral taming Of the ': Head turning during these days mag be either from or head

topt.her with head l i f t i n s the^ are combined the yolk sac, that is, the head may be turned to the

fom a mixed rnorement of the head- In case the head lift- : left Or the right But in general, t u d n g from the

inp and head turning both are extensive, the combined . sac is more frequent and more extensive than hrniog

forms a semicircular movement- '. the yolk sac. After the tenth or elemnth day, part

On the fourth day, head lifting is more. pronounced *an :; 1 Of the yo& sac is pulled over the head from the left and

head ~~t on the fifth day, head tunling is PTP a part (sometimes the whole) of the right face, making

nOunced in the of lareer embrp08, but head lifting is right and left turning of the head more diff idt , thos

Predominant if the size of the cmb;~ is small. On the i the freqnenc? and extent of the movement, =ow-

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412 413

llas a tpl&ncy to turn away from the yolk sac when the latter is ill contad wit11 its face. ~t has also a tendency to turll a,,.ay frolll tile scratching of fhe After a time, the

bill (lopclher \\-itll the head) turns to left the right face beillp ollcc more covered b?- the yolk sac. During the ,,.riggling of tilc b & ~ which will be described short1?* the head nla,- be t,risted from 10 side scvcral tinles ill succession* ill ~o,npan~- \\-it11 tllc movements Of otllcr parts the body.

Trultk mouei)ce+tts

JOua?t*L 0' -mncsn.~L m6-~, POI.. $1, l(Q. 3

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ESfBRYONIC BEHAVIOR A ~ S 415

' legs are much longer, and are partly folded down toward the breast, so that they cannot be fully extended.

It must be noted in passing that separate motions of ~e

though not independent of the motions of fie parts the leg, are observed in some cases on the sixth day alld

in case$ on the seventh day. It must. be recalled that lIl 10'2 of tile 2 1 embryos movements of the fare limbs the toes on the sixth and seventh days are rudimentarg aud

(table 4, column 13) appeared at the elld of the fourth day . m"vhO1ogicall~ not separate. On the eighth day the toes

of incubation. In the rest of the e m b ~ o s the? can move apart from each other by 2 or 3 mm. separate (but ,,itller in tile earl:- part or at the closillg of the fifth In

Tail movements . In about half' of fhe 312 embryos tail nlovcnlents appear o,,

the fourth day. 0 1 1 the fifth day active tail nlorement is in practimlly every chick. The first of

the ~ o v e m e n t is barely \*isible. I t occurs v;llrtnever the lower trunk moves- There are two kinds of tail movenlents, tile forward-and-backward movement and the sidcuvise movelllent.

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EXBRYOXIC BE&cmo~ 417

is formed. But oftentimes, fie amnion expands the bodv and may slOwly into a balloon which may remain in upanded aondi-

for to forty seconds, and then contracts slowly. This is quite a contrast to the regolar, rhythmi+ rapid, and POwerfd Wntractions and expansion of the amnion htween

side of the body. the sixth and ninth ~ Y S of incubation. ~t must be noted amnion and expansions are a]so slow and ir- regular On the fifth

and especially on the fonnh day- 4, From the tenth day on, the number of embryos which have amnion i s greatly decreased. odY a verp few chicks show amnion contractions on the thineenth and fourteenth days, and none on the fifteenth day.

The movement of the yolk sac

In spite of the fact that the yolk sac and its One of the most important factors in determining

features of the embryo, its body position, and e m b ~ O l O ~ s t s in the past hare saarcelg mentioned

the fact of suchmovements. The yolk sac has no which can and expand as does the musculature of the I t s movement is, therefore, passive; it is

. by the expansion of the amnion, but omasional~y, also, . b y the of the embryo. As incubation on, the is graduall~ absorbed and the yolk sac becomes flabby.

the chick pow8 heavier day after day, it gradually sinks the yolk sac, forming a depression. The width and depth

of the depression increase as the weight of the embrpo in-

fiw, when the amnion expands on the side of the embqO which is on the yolk sac, although the extent of the expansion greatly reduced b? the resistance of the

eqanding force is able to compregs the latter for millimeters Upon the contraction of the amnion, the

essed portion of f 01k Sac is released and returns to its nal position- AS the amnion erpands and

ically the ?oE Sac is compressed and released and aCcOrGngl~- This constitutes, in the main, the move-

ents the s a c But i n some Wsee, certain movements

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ZKXO YANQ KDO 420

There are several factors which are respmible for the '';

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swinging movement Ban does the amnion. The expanding force of the amnion together with the w e i e t of the embryo compresses the yolk sac, which, upon the release of the pres- sure, returns to its original position, thus pushing the mebryo into a swing. In support of this view, we have secured the following evidence :

1. As has already been stated, when the embryo lies with its back on the yolk sac with the belly side up, the extent of swinging is greatly increased. Now if swinbng is caused by amnion contraction alone, it ought not to be affected by changes in the position of tho body in relation to the yolk sac.

3. If a portion of the yolk is carefully drawn out without doing any in.jury to the embryo or the blood vessels of estra- embryonic circulation so that tlre yolk sac loses its elasticity and the power to return after being compressed, swinging movement is greatly diminished, although the contraction and expansion of the amnion remain unchanged. Or if a certain amount of Iiquid is injected into the yolk sac, so as to make it too compact to be compressed by the expansion of tlie amnion, the extent of swinging is similarly diminish4 in spite of the amnion contraction. .. . ------

3. If the yolk sac is held a pair of forceps and so pulled as to make its surface tense enough not to be compressed by amnion expansion, swinging either disappears entirely or is reduced to gentle rockine.

.2

1. If sainging is caused solely by amnion contraction, it must be that, a) the direction of swinging is the same as that of amnion contraction, for, as the contraction wave passes over the body, the amniotic fiuid is sqveezed forward, t ius musing the embryo to swing forward in the same direction as the contraction wave, and, b ) the amnion contraction must always be started before the swinging However, we have observed r a n g cases in which the direction of swinging is just opposite to that of the contraction wave. Moreover, two balloons may appear simuItaneously, one over the head region, the other over the tail region, and then both collapse (mn- tract) also simoltaneously toward the midregion of the body

424 . ZING 9-G EHBRyOIVIC BEHAVIOR ~m 425

the pha- and wsophaps, is also involved in such move- '%Onds)- The averaged maximum frequency of the own;ng merits, for we found that from the beginning Of the 'lapping the e)-cEd5 is given in table 2. It w~il1 be noticed that movement the stomach always contains a considerable beheen the eleventh and sixteenth days (eepeciallg after of fluid and albumen, which fact Proves that during the thirteenth d.p), frequency is re&&, oaing to the fie clapping movement (and of GOU~S% the be'' Opening during this period the eye is eneral ly covered by the the some liquid contained in the amnion- sac The table is based upon our obsemations on those

ill ,,lapping is more frequent than bill opening. One Often . embvOs whose right eye is not t)lus ~ v e r e d and on those obseTvea that every few seconds the e m b ~ o claps its in which the head of the embryo occasionally turns

times consecutirel~. I n fact, clapping Often occurs the ?ok sac. We have no idea as to ,,.heaer ind,,p,,ndentlr of other boar movements, so that dning the 'Overed eye opens and doses as frequently as it is not stages in ,yhich the embrJ.o is quiet and its acthities

'Overed b? the yolk MC. B U ~ after the ghteenth are the frequency of clapping is unaffwted' As has when this part of the yolk sac is absorbed the been previousln state& the uplifting and fowrd-thrusfing .

eye opening is increased up to hatohinge In movements of the beak appear after the pr"tmion the this it must be borne in mind Gat a t times when neck and are chiefly responsible for the piercing Of

mem- the of other parts of the bodg are in tederd

branes in hatching. ~ f " h b the environment in the egg or by fie bo&lp Of the e m b q o l the eyelids and e~eballs, and to some ex.ent

ye s~ovemefils "le beak? be the only organs that a n more freely. There are t,,5.0 types of eye movements which we have ob-

im the chick. The?:aYe m ~ ~ e ~ ~ ~ ~ ~ of the Response to rotation and tllose of the eyelids. The-latter appear much During the sninging stage, as has been stated, the

earlier than the former. ~n most cases the movement of Of the s"inging is affected by the degree rotation. But the eyeball appears bp the eighth and ninth days; in Only a a"ive bodib movements in response to the rotation of the fen cases does it occur on the seventh or the tenth The egg not Occur until after the chick has pierced ae'mem-

vhout, and its frequency of the movement is i r r e d a r throu~ "nes men lhe egg is, then, rotated so that the hatching nlngv&t~de cannot be esti-nmted "' is turned to lie ~ 6 t h the ventral sumCe domuard, it

movements of the erelids generally appear the era"?' makes some struggling mo,wments. sound is of ten day of incubation, but there are manT embvOs in rd at the =me time. The wriggling masea after a few

Tsh the rnoTe=e~t is first observed on the rids and no further reapease be repetition day. ~t the time when the eyelids begin ' rotation. many chicks, even the first rotation Produces

the of the is still e d r e m e l ~ lar@ and the response It must be noted, however, that rota- and lower are f a r away from *dl Other, s Of the egg has a great deal t.0 do arith ih e position of the spite of the movement, they wet 'Over the embqo- For details see the seventh article. erebell nntil the eleventh or twelfth day of the eyelids have been able to EoVer the it Responses to ~ O U C ~ a& pressure

most of the time, except that on omsion the When the e m b ~ o is delivered into warm physiolo@gieel kdelP opened sometimes remain open for mlution, pressme Pith a blunt needle may prodoa.

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m o Y ~ N O KUO 428 EWBYONIC BEHAVIOB h- b r ~ s 429

tion of ripper t d =cites movement of the fore lib' as nyillferference with the normal development of the as of the tun& while response to weak stimdation Of nd without changing the normal em*onic

lower trunk involve. the hind limbs and tail besides the area; 3) in the limb movement, espeaially that of bse*ation dial for estinlating quantitatively the

the hind limbs, it is often fa-d fiat when one limb is extended movements of the embryo has been devised

the oher is flexed simultane~uslf; 4) in general the move- 3. A chronolo6ieal' table of the first appearance of each

nlents of the head and of the limbs are more than those phase behavior of the embryonic chick is presented,

of the t r u d ; 3) the moveme~~t of the stimulated area 4' The of embryonic behavior in the chick stronger than that of other parts of the It seems begins from the head and progresses candad.

in certain a s e s the farther away from the " Evev movement. after its first appearan=, area the part is, the aeaker are its responses- to persist throughout embryonic life or even after '

ILBte&67 UnIes~ it is interfered m,,,jified bF7 s ~ ~ ~ , ~ regardi,rg respnclses f 0 art@&al stimuzi' tural or environrnel~tal cllanges.

rerie,,- of the abore Stat~m~ll tS rekarding responses The lifting and bending of the head are the first phrsio- logca1 respmses foulld in the chi& embryo. ~l~~~~ are later of tl,c chick embryo to different sensov stimuli, several rather tralisformd into lateral turning of the

important facts s t a d out clearly: 1) The character'stics Of

the res,,ollses to sensow stimuli are practioal1~ the mo5'emellts appear ill the later hours of the fourth Tllere are two killds of trullk movements:

name as tllosc of the movements ahich are Observed

,~tllout of externalstimuli; 2) probably the bending and extension of tile cephalic alld caudal and, 3) tile twisting of the bod!. lo sides. the of light, stinlulation of different senses

seems to forth similar reSpOnS@'s ; 3 ) in certain eases' Trunk appear after ]lead molrenlent and

. 'before ~ O ~ e m C n t s of the extremities. light alone can independent movement of the 'ye; 41 in response to sensor? stimulation the body as a is 9. Noremenis of the extremities are gellerallp found bF the

end of the fourth day. often involved; 5 ) responses to mechanical stimuli Or

of the receptors seem to appear muoh lo. appear by the foortll or fiftll dare

thall the responses to stimulation of the distance The contraction of the amnion, the morements of the

rweptors; and, 6) the response of the stimulated yolk sac? and the slv'inging movement of ille embvo begin

stronpr than those of &stant parts. ( ~ 0 ' detailed the end the fourth day and increase in freqoenep and

oion of Tarions facts see articles f o ' l ~ ~ n g this.) ma@-tude the fifth day to the ninth day, raac!ling tho by the eighth and ninth days. The frequency and

smfhUBY me@itude of these movements begin to decrease from tenth daF- Ther all disappear after the fourteenth day.

i Oral movement begins on the sixth day. lfovements are found on the seventh dsg; movements of

ball, on the ei,ohth or ninth day. brane to the air cell is rendered transparent This

one to make continuo^^ observations on the : 13. The to external stimoE, such as touch, pres- of t,be avian embvo from its earliest beginning to hatching light, and electricity, etc., are ,found in the chick

embryo in various ages.

: . , . .k

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V

=ff YAXQ KUO 430

LITERAT'GRE CITED' POW BLQ, IC. E. 1 8 ~ 1 8 3 7 Cber ~ n t r i e k l n n g ~ ~ ~ ~ ~ ~ aer Tiere.

.chtuag una Reflexion. IiBnigsb@rg.

QaaK, E. Axn E. R. 1914 o n *e early pulmtion* of the p w r i o r 'ympl'

in e l r ib embrgo, their relation to the body mOvemats. J' Eq' zoiil., 701. 17, p. 373. nTTEGUblENTAL GRAFTIXG AS A MEANS OF ANA-

cma,tL, G. E. 1929 the problem of behavior- Cambridge Uni* Ll'ZING THE FACTORS DETERbfININ~ THE

ccraitp Presk _ , ,, - _. ( . - . . _ -.. .. ----- --.- SECONDARY SEXUAL CHARACTERS ~o~o,,.i,,g ana im in the pr-t aeries =ill aPptar Is''': O F T H E LEGHORE F'OMq,l

buo, Z- T. Ontoga, of mbryonic behaaor in re*. IL The meehanieal

factors in fie rarjous leuding to h t d i n S . (To nppear in this journal.) . A. U'. POZELGb.

III. stmeld and en,.ironmentn~ factom in embr.ronjc behaTior* J-

A'al ion~l BueorcA Fellow in Biblopien? S c i m , rh i twn ~ ~ O , . a l O I I ,,I Ps;rehol. EzHmealal Zoaopy. The Cnivcrrity of clriwgo ,. ,, esd of p-nnal bcllncior upan wnnta' life- (To appeu in J'

. . Comp. Ps.vel~oI.) ,:. yc.encx eoEeept in the U ~ I I ~ of bebnvior of avian embrloo. (To ONE CHART ASD ~ l v r

in Pqchol. Rw.1 ,=. betwen benrt bent and tbc txtlavior of fie a ~ i a n embr?~. (To I. m~~~~~~~~~~ '.

a p p r aoon.) The original Pnvose of this study was to investigate.the ,.II. Exprimena, control of embrponic positions. (To app8' soon') factors determining the differentiation of intepmental struc-

tures of the fowl with reference to sex by the technique of grafting. At that time it. was not definitely know whether

. A the various secondary sexual structures ;w&u]d develop . normally when eaf ted on ,various parts, or >&at limiting -

. . . factors to this tme of experiment might exist. The fowl ma6 0riginall~ selected becaise of the marked

difference and specialization of the various seeolldaq- structures. Of laboratory animals available, none afford a neater rarietr of colltrasting sexually differentiated intep- mental structures. .

The experimental vork was first. ext'ended to all of the important external secondary sex stra?ct,nr~,s, bat, npDn the

that ~ a f t i n g of feather tissue was being studied a t another laboratory, the work was confined to the combs, wattles, and spurs. In the course of the work, certain limit- ing factors have been found which must be evaluated before the simificance of the results with reference to sex differ-

lThe -* of tbfa in~edigstion were borne in part by the Univerattp of Pittsburgh and in pa* bg the committee for ~eseareh in p,,,blema of sex of the fitional G u n d l and The Oniwrg'w of Chicago.

431

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