28 ORGANS OF SUPPORT, 



of the mouth,, where the parallel teeth composing the jaw, so 

 variable in number in the rotiferous animals, are seen at a, 

 and the insertions of the muscles at b. Sometimes only a 

 single tooth on each side is seen to compose the jaws, and 

 they have been observed to vary in the number of component 

 teeth in the jaws of different animals from one to six in each 

 jaw. Thus their most solid parts relate solely to digestion, 

 and the lightness of their exterior covering corresponds with 

 the constant and rapid movements of these rotifera through 

 their watery element. 



VIII. Cirrhopoda. The cirrhopods, like the entomostra- 

 cous Crustacea, are articulated animals enclosed in shells 

 like those of mollusca, so that they present both forms of 

 the skeleton. They have six pairs of curled jointed mem- 

 bers extending from each side of the body, from which 

 this class has received its name. Each pair arises from a 

 short thick fleshy peduncle, and the peduncle or haunch 

 of the anterior shortest pair, those 011 each side of the 

 mouth, support a pair of short, pyramidal, laminated, branchiae, 

 like those attached to the haunches of the legs in most of 

 the Crustacea. The feet are covered externally with a trans- 

 parent, firm, elastic integument, are regularly and closely 

 jointed to their finest extremity, and are furnished with 

 minute jointed cirrhi disposed along each side of their inner 

 concave surface. The trunk of the body between the feet 

 is also partially jointed ; it presents the usual nervous 

 columns and ganglia disposed along the ventral surface, as in 

 other articulated classes ; and, as in them, the intestine 

 passes straight from the mouth to the anus, which opens into 

 a long thin flexible conical tube. The mouth of these ani- 

 mals is furnished with an upper and a lower lip, with a pair 

 of mandibles and a pair of maxillae. The maxillae are fur- 

 nished with small fleshy palpi, and the lower lip is formed 

 by the union of the exterior maxillae. The cirrhopods are 

 almost always inclosed in multivalve shells secreted from the 

 outer surface of a fleshy, thin enveloping mantle, and which 

 are attached to submarine bodies either directly by their 

 base, or by means of a fleshy tubular peduncle. These 

 exterior shells are generally thin, laminated, dense, composed 

 of carbonate of lime with animal matter, and grow by the 

 successive addition of layers to their inner surface. The 



