Phylogeny of Animals 535 



trace them back to an originally single dorsal shield, like that 

 of Apus." Much may be said for both views, but till accurate 

 study of the center or centers of origin for the rotiferan dorsal, 

 ventral, and lateral plates of the lorica has been made it would 

 be vain to say more. But the relation to lorica-formation 

 in rotifers is most suggestive, except that from their usually 

 active habits Crustacea do not appear to form a ventral shell, 

 though even this may yet be recognized in the "sternal" ele- 

 ment of crustacean calcification. 



In passing to the internal organization attention may first 

 be drawn to the comparative details of Figs. 25 a and b; that 

 represent an adult rotiferan and a larval entomostracan phase. 

 But, in the succeeding account, adult points of structure in the 

 divisions of both classes will be referred to. 



The mastax of rotifers is reproduced more or less perfectly 

 throughout the whole crustacean series, and the teeth or spines 

 of this "gastric mill" show surprising agreement as to structure 

 and function in both. In Bairdia and some of the Phyllopoda, 

 the chitinous plates are either styliform, bristle-like, or toothed 

 and triturating, but in the highest division that includes the 

 crabs and lobsters the entire system consists of a median plate 

 resembling the incus of rotifers, and sets of lateral plates that 

 work on it after the manner of the unci and manubria of rotifers. 



The sections and the glands of the alimentary canal agree 

 at least in their connections in both. The brain or dorsal 

 ganglion is of like origin and position, and bears a like relation 

 to the eyes, and the antennules or dorsal antennae. But, till 

 greater detail is secured for Rotifera, it seems impossible to 

 correlate the suboesophageal ganglia and nerves in both classes. 



A character that may be said to be largely diagnostic of 

 the rotifers is the median anal spine, and even more constantly 

 of the paired spines borne on each side of the median one. 

 They may vary in size, length, and degree of flexible movement. 

 They seem to be the precursors and homologues of the telson 

 and anal spine of Crustacea. But we have already noted that 

 two cement glands are developed within and open on these 

 pedal processes, and further that, as this pedal portion expands 

 in Brachiopoda, Polyzoa, and Mollusca, the glands are very 

 often developed, while their viscous secretion is used in several 

 ways. If then the processes of the telescopic foot in Rotifera 

 correspond to the telson segments in crustaceans, one might 

 hope — even expect — to find cement glands in these. 



The writer has searched in vain for any record of them. 

 Frequent mention is made of viscous excretions in the Cope- 

 poda and Ostracoda, while the cementing of larval acorn shells 



