^ 130. THE ROTATORIA. 141 



BOOK SEVENTH 



EOTATOIUA. 



CLASSIFICATION. 



§ 130. 



The body of the Rotatoria is covered with a smooth, hard epidermis, 

 and, from transverse incisions, at least at its posterior portion, usually ap- 

 pears articulated ; while its anterior portion has vibratory retractile parts — 

 the so-called rotatory organs. The very indistinct nervous system is almost 

 wholly comprised in a cervical ganglionic mass. The fully-developed digest- 

 ive canal lies in the large cavity of the body, and its anterior portion is 

 provided with masticatory organs, while posteriorly, it terminates in an 

 anus. Female genital organs alone have as yet been found with certainty. 



No one would deny that the Rotatoria, whose organization is so high, 

 ought to be separated from the Infusoria, whose structure is scarcely advanced 

 above that of a simple cell-nature. One can be in doubt only as to their 

 other and proper place in the animal kingdom ; — whether, with Burmeister, 

 they are to be placed among the Crustacea ; or with Wieg^nann, Wagtier, 

 Milne Edwards, Berthold, and others, among the Worms. But the choice 

 here between these two classes will not be difficult, for, as will soon be shown, 

 they differ widely from the Crustacea. Aside from the absence of a ven- 

 tral cord and of striated muscular fibres, these animals have vibratile or- 

 gans upon the surface of their body, as well as upon their respiratory and 

 dicjestive organs — a structure not found with the Crustacea, nor with the 

 Arthropoda in general. Their development is non-metamorphotic, and 

 they do not have articulated feet when they escape from the egg ; while 

 the Crustacea, and even those which, from a retrograde metamorphosis, be- 

 come vermiform, have at least three pairs of articulated legs when hatched. 

 On the other hand, they have, in common with most worms, an articulated 

 body, internal and external vibratile organs, absence of a ventral cord, 

 and, with all, the want of articulated feet. 



Although the uniformity of their organization does not admit of these 

 animals being divided into orders, they can at least be considered as a sep- 

 arate class in the great section of Worms. 



