The Vascular System of StylodrilusAuthor(s): Rowland SouthernSource: The Irish Naturalist, Vol. 17, No. 11 (Nov., 1908), pp. 238-239Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25523348 .

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238 The h ish Naturalist November,

NOTES ON THE DISTRIBUTION OF IRISH FRESHWATER (MITES HYDRACHNID.E).

BY J. N. HAUBERT, M.R.I.A.

The mites in general are among the most widely distributed animals, and the Hydrachnidae are no exception to the rule. The winged insect hosts to which these mites attach them sel ves during their parasitic larval stage are very effective agents in the spreading of the species. It has been suggested that the freshwater mites may be divided into two great faunistic groups, according to the nature of the waters they inhabit, and these two divisions serve equally well for a

preliminary grouping of the Irish species from a distributional point of view. One group con tains those widely distributed species inhabiting the

standing and

slowly-flowing waters of lowland lakes, ponds, etc., of a comparatively

high temperature. To the second group belong those interesting forms found in waters of a constantly lower temperature, especially those of cold highland lakes and streams. These forms possess a more restricted range, typically northern and alpine in character, reaching their

greatest development in Scandinavia and the alpine regions of Central

Europe.

THE DEVELOPMENT OF LITTORINA.

BY W. M TATTERSAr.L, M.SC.

The eggs of L. litorea, each enclosed in a hat-shaped capsule are laid

freely on the shore, not aggregated together in a gelatinous mass. There are trocosphere and veliger larval stages. /.. litorea lives low down in the zone of Laminaria and Fucus serratus. L. obtusata lives higher among

Fucus vesiatlosus ; its larva leaves the egg as a veliger. I. rudis and /.. neritoides which live near high-water mark are both viviparous. Thus the genus exhibits three stages in the evolution of land from marine mo?lusca, with the suppression of larval forms with successive

sp?cialisations of habitat.

THE VASCULAR SYSTEM OF'STYLODRILUS.

BY ROWLAND SOUTHERN, B.SC.

The genus Stylodrilus has hitherto been distinguished from other

European genera belonging to the Oligochaete family Lnmbriculidae

by the complete absence of the blind contractile appendages of the blood

vessels which are so characteristic of this family. The new species in

vestigated (but not yet described) from the River Annalee, County Cavan,

undoubtedly belongs to the genus Stylodrilus, but differs from all other

species in the possession of very simple contractile appendages to the

dorsal vessel. These blind sacs are restricted to the posterior end of the

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i9o8. The British Association in Dublin. 239

worm, and are simpler in structure than those of any other Lumbriculid.

This species thus forms an interesting link between the normal Lumbri

culid type and the aberrant genus Stylodrilus. The relations of the

dorsal and ventral vessels to the intestinal blood-sinus are also in

vestigated, and shown to differ considerably from the condition typical of the Oligochseta.

SECTION E.?GEOGRAPHY.

IRELAND?HER COASTS AND RIVERS.

BY REV. W. SPOTSWOOD GREEN, C B,

This paper described the succession of events in the geographical

history of Ireland from the time that the river valleys were being

sculptured and the present configuration of the country determined

through the great Arctic and forest periods to the coming of man into

the island, the evolution and admixture of races, and finally dwelt upon the beauty spots with which Ireland abounded, and which the author

hoped that many who had come to the British Association might go and

see for themselves.

MITCHELSTOWN CAVE.

BY C, A. HILL, M.A., M B.

Mitchelstown C^ve, the largest yet discovered in the British Isles, is

situated in County Tipperary, in the valley of the Blackwater. There

are actually two separate and distinct caves. The existence of one, the

"old" cave, is now forgotten, though this cave was known and exhibited

in 1777. The "new" cave, first discovered in 1833, is now the only one

shown to visitors. It was first described by Dr. Apjohn, of Dublin, who

partially explored and surveyed it in 1834, and published a map, which

has been the basis of all others up to the present time. It was further

explored by M. Martel, of Paris, in 1895, and described by him, and was

also visited by Dr. Lyster Jameson, of Dublin, who described the cave

fauna found therein. Very little is known of the full extent of the caves

even at the present day, and no reliable plan or map exists.1 The cave

was visited in 1905 by the author, who took many photographs, now

shown for the first time, and also explored portions hitherto unvisited.

The cave was found to be of much greater extent and complexity than

was previously imagined. There is great need for systematic exploration and surveying, as the

existing plan of the "new" cave has been found inaccurate and mis

leading, and practically nothing is known of the "old" cave. Geologi

cally the " new

" cave is of great antiquity, as evinced by the enormous

1 The cave has been since thoroughly explored and mapped by Dr.

Hill, Dr. A. Rule, H. Brodrick, and R. LI. Praeger. An account will

shortly be published in the Irish Naturalist.

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