141

The cuticle of cysticerci of Taenia saginata, T. hydatigena,and T. pisiformis

By E. H. SIDDIQUI(From the Sub-Department of Parasitology, Department of Zoology,

University of Edinburgh, West Mains Road, Edinburgh, 9)

With 3 plates (figs. 1 to 3)

SummaryThe structure of the cuticle of the cysticerci of 3 species of Taenia was studied bymeans of optical and electron microscopy. In all 3 species the cuticle is composed of3 layers and covered with hair-like processes. The middle layer, which comprises thebulk of the cuticle, varies in thickness from head to bladder, but there are no differencesin thickness between the species studied. The hairs are composed of a core representingan extension of the middle layer and are covered by a continuation of the outer layer.The arrangement of these hairs varies in the species studied.

IntroductionT H E cuticle of cysticerci has been described by several investigators (Leuckart,1886; Young, 1908; Crusz, 1948; Holz and Pezenburg, 1957; Voge, 1962).Their accounts differ, however, with regard to the number of layers formingthe cuticle, the nature of the hair-like processes, and the relation of these hairsto the cuticle and subcuticular tissues. Leuckart (1886) referred to earlierdescriptions of superficial hairs in Cestodes, but attached no importance tothem. Young (1908) noted the hairs on Cysticercus pisiformis and suggestedthat they were extensions of parenchyma fibres, while Holz and Pezenburg(1957) thought that the hairs in C. bovis originated from minute granulessituated beneath the cuticle, although such a connexion was not actually demon-strated. The present study with the optical and electron microscopes was under-taken with the aim of resolving the differences appearing in extant descriptions.

Materials and methodsThe whole of the material of C. bovis (Taenia saginata) was obtained from

a single bullock, slaughtered in the Edinburgh abattoir, which had a severegeneralized infestation. All the cysts used in the present investigation weretaken from the masseter muscle, from which 49 cysts were recovered.

C. tenuicollis (T. hydatigena) is abundantly available from abattoir sheep.It was collected from the mesenteries on several occasions.

C. pisiformis was recovered from the mesenteries of rabbits maintained inthe laboratory, 8 weeks after ingestion of T. pisiformis eggs collected from anexperimentally infested dog.

For optical microscopy the cysticerci were always freed from their capsulesbefore fixation. The following fixatives were used: Helly, Bouin, Carnoy,

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142 Siddiqui—Cuticle of cysticerci

Flemming (Baker, 1945; Pantin, 1948). The period of fixation for the first twofixatives was 6 h and for the last two 2 h. After thorough washing and removalof excess fixative the cysticerci were dehydrated as far as 96% ethanol and thentransferred to a 1:1 mixture of 96% ethanol and methylbenzoate. They werethen passed through methylbenzoate to pure benzene and embedded in paraffinwax. Sections were cut at 5^, and stained with Ehrlich's haematoxylin andeosine, Heidenhain's iron haematoxylin, or Mallory's triple stain (G. T. Gurr).

For electron microscopy the cysts were opened and pieces of tissue approxi-mately 2 mm square were excised and fixed in buffered osmium tetroxidesolution (Palade, 1952). After dehydration in ethanol and infiltration withra-butylmethacrylate they were embedded in a mixture of 93 volumes ofn-butylmethacrylate and 7 volumes of methylmethacrylate, to which 1% (w/v)of benzoyl peroxide had been added as catalyst. Tissues were sectioned atapproximately 25 m/x with a Huxley ultramicrotome, and examined witha Siemens elmiskop I electron microscope.

ResultsC, bovis. The thickness of the cuticle appears to be independent of the size

of the cyst. The present material ranged from 4 mm to 7 mm in majordiameter. This variation in size largely reflects differences in the stage ofdevelopment reached, since the larger cysts possessed more completely deve-loped suckers than the smaller ones. Within the individual there is markedvariation in cuticle thickness, ranging from 5 yt, over the invaginated head downto i/x over the bladder, with a gradual transition between. Three distinctlayers are readily distinguished in the cuticle of sections stained with Mallory'striple stain, which colours the external and basal layers blue and the middlelayer red.

The external layer is very thin and was found to be loose or absent over thehead in the larger cysts. The middle layer is homogeneous in appearance andforms the bulk of the cuticle. It is this layer which varies markedly in thick-ness and so produces the differences described in total cuticle thickness.Beneath this layer there is a basal layer of thin fibres; this is always distinct.Both the haematoxylin methods used dyed the cuticle uniformly, withoutdistinction between the 3 layers.

FIG. 1 (plate). T. saginata (C. bovis). All preparations are from a single individual, A to D,photomicrographs of sections fixed in Helly and stained with Mallory.

A, part of the head, showing cuticle (c) consisting of the middle (ml) and basal layers (W)only, and subcuticular tissues (sc) with nuclei (n).

B, part of the cuticle (c) of the developing head, showing all three layers, external (el), middle(ml), and basal (bl).

c, cuticle (c) of bladder with superficial hairs (h). The cuticle here is much thinner than onthe head. Im, longitudinal muscle.

D, section of bladder more distant from the head than c, showing still thinner cuticle (c) andshorter hairs (h). Im, longitudinal muscle.

E, electron micrograph of cuticle, showing the relative thicknesses of the 3 layers and thestructure of the superficial hairs (h). The vacuolation evident in the middle layer may be aaartifact.

FIG. I

E. H. SIDDIQUI

FIG. 2

E. H. SIDDIQUI

Siddiqui—Cuticle of cysticerci 143

The surface of the cyst in this species is densely covered by fine hairs whichvary in length from about 2/x to 4JU,. They are longer on those parts of thecuticle which have the middle layer thicker, except on the invaginated cuticleof the head, where they are always lacking (fig. 1, A, B). The structure of thesehairs is not discernible with the optical microscope on account of their pooraffinity for stains.

Under the electron microscope the middle layer is found again to be themajor component lying between very thin external and basal layers. Thestructure of the superficial hairs is now manifest. The middle layer is drawnout into fine villiform processes, over which the external layer is continuous.Thus the hairs are made up of two of the cuticular layers (fig. 1, E).

C. tenuicollis. The structure of the cuticle of this species is essentially similarto that of C. bovis. The 3 layers, their variation in thickness, and the superficialhairs are all shown in fig. 2, A to E. The hairs appear to be somewhat longerthan in C. bovis; they are sparser and more widely spaced.

C. pisiformis. The main feature of this species is the discontinuous distri-bution of the superficial hairs. These are much sparser than in the 2 previousspecies and are confined to irregularly scattered groups. They are, moreover,much shorter than in the other 2 species. Whereas the cuticle in C. bovis andC. tenuicollis is quite smooth, that of C. pisiformis is thrown into furrows insome places, and in these the hairs are absent.

It is remarkable that the thickness of the cuticle is about the same in all 3species described, although the cysts themselves differ greatly in size. Thusthe cuticle is of about the same thickness in cysticerci of C. bovis 5 mm long,of C. pisiformis of some 10 to 12 mm, and of C. tenuicollis measuring 40 mmor more.

DiscussionYoung (1908) in his studies on the histogenesis of C. pisiformis recognized

2 cuticular layers, of which the outermost was sometimes missing. His use ofhaematoxylin, however, which we find to stain all cuticular components uni-formly, may account for his failure to recognize all 3 layers of the cuticle.Crusz (1948) and Voge (1962) both describe the cuticle of C. tenuicollis as asingle-layered structure, which stains blue with Mallory's triple stain. Thisresult is quite different from the present findings, in which the predominantcolour (middle layer) is red with Mallory's stain. This difference must beattributed to differences in technique, since, according to Pan tin (1948), differ-ences in manufacture of the dyes and in timing and procedure produce con-siderable variation in results. Voge (1962) identified a thin blue layer beneath

FIG. 2 (plate). T. hydatigena (C. tenuicollis). All preparations are from a single individual.A to D, photomicrographs of sections fixed in Helly and stained with Mallory.

A, head region.B, neck region.C and D, bladder region.E, electron micrograph showing sparser distribution of hairs than in C. bovis. Lettering as in

fig. I.

144 Siddiqui—Cuticle of cysticerci

the cuticle; this may correspond to the basal cuticular layer of the presentwork. On the other hand, Holz and Pezenburg (1957) positively deny theexistence of a basement membrane beneath the cuticle and describe a con-tinuity between cuticle and underlying cells mediated by fine intercommuni-cating cellular processes. Such structures were never observed in the presentstudies, in which the triple-layered structure of the cuticle observed with thelight microscope was confirmed by electron microscopy. Holz and Pezenburgalso attempt to relate the superficial hairs to the fine subcuticular filamentousprocesses they describe. Young (1908) thought that the hairs provided ameans of direct communication between the subcuticular tissues and theexterior. However, the precise structure and relations of the hairs cannot beresolved with the light microscope. Electron microscopy shows quite clearlythat the hairs are derivatives of the middle cuticular layer and are covered bythe continuous external layer, but there is no evidence for the continuity withsubcuticular structures described or postulated by earlier workers.

It is interesting to note that Ludvik (i960) demonstrated similar hair-likeprocesses on the cyst wall of Sarcocystis miescheriana by electron microscopy,and suggested for them a possible nutritional role by increasing the surfacearea of the parasite. If a similar role be postulated for the hairs of cysticerciit perhaps becomes significant that in the species where hairs are sparsest,namely C. pisiformis, the cuticular surface is increased by a distinct furrowing.

This work was financially supported by the Colombo Plan authorities in theUnited Kingdom, to whom I am greatly indebted. I thank also the membersof the staff of the Parasitology Sub-Department at Edinburgh, and Dr. J. R.Baker, F.R.S., of the Department of Zoology, Oxford, for their guidance andencouragement. Finally, I am most grateful to Dr. D. C. Barker and Mr.A. E. G. Dunn for carrying out the electron-microscope procedures.

ReferencesBAKER, J. R., 1945. Cytological technique. London (Methuen).CRUSZ, H., 1948. J. Helminth., 22, 63.HOLZ, J., and PEZENBURG, E., 1957. Monats. Tierheilk., 9 (2), 37.LEUCKART, R., 1886. The parasites of man. Edinburgh (Pentland).LUDVIK, J., i960. J. Protozool., 7, iz8.PALADE, G. E., 1952. J. exp. Med., 95, 285.PANTIN, C. F. A., 1948. Notes on microscopical technique for zoologists. Cambridge (University

Press).VOGE, M., 1962. Proc. helm. Soc. Wash., 275, 32.YOUNG, R. T., 1908. Zool. Jb. (Abt. 2), 26, 183.

FIG. 3 (plate). T. pisiformis (C. pisiformis). All preparations are from a single cyst. A to D,photomicrographs of sections fixed in Helly and stained with Mallory.

A, head region.B, neck region.c and D, bladder region.Note the furrowing involving all layers of the cuticle in sections B, c, and D, and the super-

ficial hairs disposed in groups in section c but absent from B and D.E, electron micrograph. Lettering as in figs. 1 and 2.

FIG. 3

E. H. SIDDIQUI