shape can be more or less altered, enabling some species ta crawl about like a leech. Other muscles assist the movements of the ciliated wreath, as well as those of the tail-foot. Under careful illumination I have occasionally observed muscular striæ.
The body-cavity, with its various internal organs, is protected by an integument of greater or less firmness, shaped like a shield, a boat, a spindle, a vase, and so forth, in those cases where the integument is hardest, it may be termed the lorica, corresponding to the carapace of Enntomostraca, and having a similar chitinous composition. Its surface is bare of cilia, but it is not infrequently armed with lateral or terminal spines. The only approach to an articulate appendage possessed by Rotifera is that which I have called the tail-foot. It is not a prolongation of the back, and is, therefore, not a true tail. Coming off from the under surface of the body, below the anal orifice, it may be regarded as a kind of foot. It is capable of being shortened, either on the telescopic principle, or, when soft, by contracting in wrinkles. The basal portion varies considerably in length, being reduced sometimes to a mere stump. At its narrower end are often inserted, movably, one, two, or three styles, or dagger-like bristles, which may be very long. When these are two in number, they strongly remind us of a pair of scissors; when they are three, the middle one is small. With this organ the Rotifers steer themselves in the act of swimming, or hold on to some support while groping about for food, or even, in a few instances, take veritable leaps.
With regard to reproduction, the same phenomena of parthenogenesis have been observed, which we noticed when describing the Entomastraca. The young are born from two very distinct kinds of eggs; the summer eggs, which are generally, if not always, virgin produce; and the Winter eggs, which have been duly fecundated. The latter are preserved against the cold by a peculiar shell, tl spring returns to hatch them. While the females multiply in enormous numbers, the males are very rarely met with. The latter, moreover, are, as a rule, so unlike the former in appearance, that it is difficult to recognise them as belonging to the same species. It is a curious fact, that in all males the alimentary canal is either absent or rudimentary. Whey are, consequently, short-lived.
Before briefly considering particular examples of Rotifera, I will here give my authorities for the preceding anatomical sketch, while naming a few works to which the student can refer for a fuller account of the subject. He will find that the ablest observers are by no means unanimous on many important points in the anatomy and life-history of these somewhat puzzling animals.
Works of reference:—Pritchard's "Infusoria;" Rolleston's Forms of Animal Life;" Huxley's "Anatomy of the Invertebrated Animals;" Gosse's "Papers in the Philosophical Transactions."
To be continued.
