44 
BULLETIN OF THE LABORATORIES 
orly in a several-jointed abdomen or “foot,” which bears two caudal 
stylets and contains glands which secrete a gummy fluid used by the 
animal in temporarily adhering to other objects. The form varies 
from nearly spherical or round lense-shaped to terete and extended. 
The cuticle is modifided in various ways, sometimes appearing like a 
bivalve shell and thus hightening the resemblance to certain entomos- 
traca and explaining why older naturalists classed the rotifers under 
Crustacea. The cuticle may be smooth or beautifully ornamented and 
produced into long spines or marked off into areas outlined by im- 
pressed or raised lines. The cuticle is secreted by a hypodermic layer 
which is often seen obviously to consist of cellular tissue. Notwith- 
standing the protection afforded by a chitinous shell, some species 
(as Melicerta ringens) build for themselves a tube composed of ma- 
terials gathered from the water and apparently connected by a cement 
secreted in a gland near the mouth. Such an envelope may be com- 
pared to those swallows’ nests eaten in Asia, or the case of a caddis-fly. 
Some of the species live in colonies, and when the colony is spherical, 
as in Coitochilus, it is a veritable microcosm — a sphere of active, vora- 
cious creatures whirling through aqueous space. In only one case is 
it certainly known that a moult takes place, and facts seem to be un- 
harmonizable with the theory that such a change of coats is affected. 
The cilia of the trochal disc or “wheel” are arranged in the 
greatest variety of ways in different genera. The attempt is made to 
refer all these forms back to a fundamental form — i. e. a double circlet 
of cilia, the outer of which is largest and serves as locomotory, while 
the inner set is under the control of voluntary nerves and serves simply 
to bring food within the pharynx. In many cases there is really no 
indication of such a distribution and the cilia seem to be merely iso- 
lated clusters of hairs scattered about the oral end of the body. 
Several of the rotifers are parasitic and cling to the less exposed parts 
of the body of certain Amphipods, or on Annelides, or are endopara- 
sitic. The muscles are often very conspicuous and, when large, show 
the striated structure well. The alimentary canal, maxtax, and the 
contractile water vessel have muscular tissue af another sort. 
The nervous system is most difflcult to study and little is certainly 
known of its structure. Usually there can be made out a considera- 
ble granular mass over the maxtax and in close proximity to 'the eyes, 
this is assumed to be the principal ganglion. From the chief or cen- 
tral ganglion fine nerves pass to the muscle and organs of sense. 
