THE TARDIGRADA OF THE SCOTTISH LOCHS. 689 
they may be present in some individuals of a species and not in others. The fat-cells 
in the body-fluid have a characteristic colour; in most species they are clear and 
hyaline, but in a few they are golden yellow or dark brown. 
The segments of the body are superficial, affecting the skin only. There appear to 
be usually two segments to the head, one to each pair of limbs, and intermediate 
segments—ten in all; but they are often increased in number by subdivision, and there 
are very commonly two between the third and fourth legs. 
Simplex Forms (15).—Individuals of species of Macrobiotus are often found which 
exhibit a remarkable reduction of the masticating apparatus: the teeth are straight, 
without stays—they are not functional; the rods of the pharynx disappear ; in extreme 
cases, the mouth and gullet are quite obliterated. This state can only be temporary, 
or the animals would die; and they often appear in good health, and may have the 
stomach filled with food. I can only suggest that it is temporary, and a preliminary 
to moulting ; but if this is so, it is a remarkable parallel, among animals so high in the 
scale, to the disappearance of the mouth in ciliata during fission. 
In exceptional cases, the pharynx and teeth entirely disappear. 
Reproduction.—Two forms of eggs are laid, the one kind round and spiny, the 
other smooth and oval or elliptical. The spiny eggs are laid singly and free; the 
smooth eggs are laid in the moulted skin, which serves as a protective capsule for them. 
So far as known, the same species always lays the same kind of egg. The smooth and 
spiny eggs are not, as from analogy we would expect, the summer and winter eggs of 
the same species ; but further observation on the point is needed. The laying of smooth 
eggs in the cast skin is the prevalent mode of reproduction in the genus as in the order. 
It is very difficult to trace which species lay spiny eggs, as, for some unexplained 
reason, animals containing such eggs are very rarely seen. When the young contained 
in the smooth eggs are ready to hatch, it is seen that the teeth and pharynx are very 
large and fully developed. The stiletto-like teeth are continually apphed to one spot 
in the shell till they weaken and finally pierce it. At this stage the pharynx is not 
very greatly inferior in size to that of the mature animal, and the characteristic 
thickenings are all present. 
Two groups of species are to be distinguished in the genus. The first, typified by 
M. hufelandi, have the two pairs of claws similar, the claws strong, the claws of each 
pair rigidly united and one of them slightly larger than the other, the larger claw of 
each pair with a strong supplementary point. The second group includes species 
having the two pairs of claws dissimilar, slightly united at the base only, the larger 
pair having one very long slender claw and a much shorter one, the other pair similar 
but smaller, or of two nearly equal claws—supplementary points none, or very 
fine. 
I believe all species of the first group lay spiny or viscous eggs ; those of the second, 
smooth eggs enclosed in the skin. The species having two single claws and a pair form 
an extension of the second group. 
