68 GENEKAL HISTORY OF 



the manner of the Daphnia or water-fleas, by the action of bristle- 

 like appendages, ex. Triarthra. 



On these varieties of the movements of Rotatoria it is, that 

 M. Dujardin bases his primary divisions of the class. 



Section XX. — Of the External Coverings, of the Muscular System, 

 and of the Organs of Locomotion of Rotatoria. — The external surface 

 of Rotatoria is made up of a smooth and firm integument, more 

 delicate at the anterior extremity or head of the animals, where it 

 becomes ciliated. Its contractions coincide with those of the sub- 

 jacent parenchyma, whence it is not drawn into folds. In many 

 instances the integument presents transverse or circular markings, 

 indicating the division of the body into segments, as in the Crustacea. 

 The usual smooth condition of the integument is departed from in 

 the genus Choetonotus, (figs. 357-358) and in Philodina aculeata, (figs. 

 487-489) the surface is strewed with stiff bristles and styles — ^whilst 

 that of Noteus (figs. 491-494) and of some Anurwa, is roughened by 

 granular eminences. 



The caudal extremity exhibits the transverse wrinkles most 

 strongly, and in many cases is clearly divided into segments, as in 

 Conochilus, (figs. 365-370) Megalotrocha, (figs. 374-375) Lacinula/ria, 

 Noteus, &c. In various species of Hydatina, Rotifer, Eosphora, 

 Philodina, &,x., not only the caudal portion, but the rest of the body, 

 is also divided into segments, which will slide upon one another Like 

 the tubes of a telescope. 



A rigid horny shield, resembling, in structure, that of Daphniae, 

 is met with in Brachionus, Anuroea, Noteus, &c. Within the outer, 

 firmer tunic, Mr. Gosse describes an inner, softer one, into which the 

 muscular cords are inserted. (See those families.) 



Some Rotatoria possess, besides the integument immediately in- 

 vesting them, another external to it, and surrounding it in the form 

 of a sheath, to the bottom of which they are fastened. This sheath 

 (urceolus) varies in kind as well as in form ; thus, in Lacinularia (fig. 

 378) it is gelatinous, and the animal imbedded in it; in Melicerta, 

 (figs. 386-387) the animal can move freely within its gelatinous 

 case, which is here strengthened by adherent foreign particles, the 

 same, in a less degree, obtains in Oecistes (fig. 362) ; and in Zinmiaa, 



