XIX ANATOMY 479 
for histological research. One way to produce the above-men- 
tioned stillness is partly to asphyxiate the animals by placing 
them in water which has keen boiled, and covering the surface of 
the water with a film of oil. 
The whole body is enclosed in a thin transparent cuticle, 
which must be pierced by a needle if it be desired to stain the 
tissues of the interior. As a rule the cuticle is of the same 
thickness all over the 
body, but im the genus 
Echiniscus the cuticle 
of the dorsal surface is 
arranged in thickened 
plates, and these plates 
are finely granulated. 
From time to time the 
7 : G Fic. 251.—Zchintscus spinulosus, C. Sch., x about 
cuticle is cast, and this 200, seen from the side. (From Doyére.) 
is a lengthy process, so 
that it is not unusual to find a Tardigrade ensheathed in two 
cuticles, the outer of which is being rubbed off. The Macro- 
bioti lay their eggs in their cast cuticle (Fig. 250). The end of 
each of the eight legs bears forked claws of cuticular origin. 
The legs are not jointed except in the genus Lydella, where two 
divisions are apparent. 
Within the cuticle is the epidermis, a single layer of cells 
arranged in regular longitudinal and transverse rows along the 
upper and under surface, where the cells are as uniformly 
arranged and as rectangular as bricks. The cells on the sides of 
the body are polygonal, and not in such definite rows. The nuclei 
show the same diagrammatic symmetry as the cells which con- 
tain them, and lie in the same relative position in neighbouring 
cells. In a few places, such as the end of each limb and around 
the mouth and arms, the cells of the epidermis are heaped up 
and form a clump or ridge. In some genera a deposit of pig- 
ment in the epidermis, which increases as the animal grows old, 
obscures the internal structures. It is generally brown, black, 
or red in colour. 
The cuticle and epidermis enclose a space in which the various 
internal organs lie. This space is traversed by numerous 
symmetrically disposed muscle-fibres, and contains a clear fluid— 
the blood—which everywhere bathes these organs. This fluid 
