678 MR JAMES MURRAY ON 
In the preparation of this paper | have been greatly indebted to Mr D. G. ScourFIELD, 
and to Prof. Ricurrers of Frankfort, who kindly consented to examine my drawings, and 
assisted me with advice, and with literature to which I had not myself access. Without 
this willing help the considerable material at the disposal of the Lake Survey could 
not have been utilised. 
References to the bibliographical list are throughout the text made by figures 
enclosed in parentheses, thus (1), (15). 
The animals are all drawn to the same scale, so that their relative sizes may be 
seen. The principal measurements are given both in fractions of an inch and in 
microns. For convenience of reduction the inch is taken as equal to the round 25,000 
microns, which is a near enough approximation for practical purposes. 
STRUCTURE. 
The Tardigrada are articulated animals, regarded as having their nearest relatives 
in the Arachnida. 
The structure is only treated here in so far as is necessary for systematic purposes. 
Water-bears are segmented animals, having four pairs of joimted legs, the segmenta- 
tion of both body and limbs very obscure and superficial. The blood consists simply 
of a body-fluid, filling the whole of the body cavity between the skin and the alimentary 
canal. In the body-fluid are usually numerous large nucleated cells, formerly regarded 
as blood-corpuscles, but now called fat-cells (13); small dark granules may also be 
present. ae 
Skin.—This may be smooth and hyaline, pigmented, papillose, warted, or spiny, 
indistinctly segmented or thickened dorsally and formed into a series of protective 
plates, symmetrically arranged (Hcehiniscus). 
Legs. —There is usually a distinct basal portion of each leg, the skin of which seems 
to be an extension of that of the body, forming a kind of sheath for the leg proper; two 
joints may sometimes be distinguished in this. There may be one or many claws on 
each leg, which may all be free, or united into groups of two or three. 
Head.—Two joints, sometimes three, are distinguishable in the head. There may 
be many palps and sete on the head, or none; eyes may be present or absent; there 
may be a rostral prolongation, or not. 
Masticating Apparatus.—This is somewhat elaborate, the food being acted upon by 
two sets of organs which function as teeth. The teeth proper are a pair of straight or 
curved rods, looking very much like chop-sticks, tapering in front to very fine stiletti- 
form points which enter the mouth, a short, funnel-shaped expansion of the anterior end 
of the alimentary canal, or the throat, a narrowed portion of the tube, separating the 
mouth from the gullet. These stiletto-like points pierce the cells of the plants or 
animals which serve as food, which are then sucked. The teeth are much enlarged 
posteriorly, and usually forked; they may be connected with the gullet by supports 
