Phylogeny of Animals 529 



terest, could the embryology of such a primitive organism 

 of the class as Nautilus have been before us. In want of such 

 the recent members of this great class have evidently become 

 so highly modified, even in the early larval stages, that it would 

 be inopportune now to attempt the tracing of their phylogeny. 



The Polyplacophora or Amphineura seem to have a history 

 that constantly wavers in its earlier phases between the anne- 

 lidan and molluscan lines, but eventually ends toward the 

 latter. The later larval stage, described and figured by Kow- 

 alewsky, shows marked agreement in detail wnth the rotifer 

 Dinocharis, and specially D. Collinsii. In both the organism 

 is dorsally arched and ventrally somewhat flattened, in both 

 transverse areas are early indicated that suggest six to eight 

 transverse plate segments, in both an anterior head plate 

 arises; setae that project through the cuticle or lorica are 

 arranged transversely, the test early shows fine spots or mark- 

 ings, the details of which we are still ignorant of for Dinocharis, 

 but which develop the aesthetes and possibly eyes in Chiton. 

 A minute examination and comparison here is very desirable. 



Further in both the alimentary canal is somewhat arched 

 but straight, the eyes are situated rather far back, while many 

 other points of agreement with typical rotifers are revealed. 



We may sum up then by saying that the various molluscan 

 divisions show, from the trochophore and veliger stages on- 

 ward, so many fundamental points of agreement with definite 

 living genera of rotifers, that these can all be exactly accounted 

 for if we bear in mind that living rotifers are long-drawn de- 

 scendants doubtless from once greatly more abundant and 

 varied genera, forms of which would equally have united the 

 living with the extinct, and would as perfectly have furnished 

 connecting types between themselves and the Mollusca, as 

 well as other great divisions. 



The Arthropoda now remain for consideration. By many 

 zoologists it is now recognized tliat the Rotifera, Chcetophora, 

 and Articulata form divisions that are fundamentally inter- 

 related, and all distinguished by the tendency to produce 

 bristles on the surface of the body, or on special expansions 

 of the body. But, though Gosse has very clearly stated that 

 he regards the rotifers and crustaceans as near allies, many 

 have rejected such a view. So the remarkable genus of roti- 



