GENERAL CONSIDERATIONS. 171 



in the Chaetodermatina and as is well known this latter organ is practically 

 straight. In the Neomeniina it is unique in possessing an anterior dorsal coecum 

 that extends forward to the neighborhood of the brain; and the liver is not 

 sharply differentiated from the gut. The opening of the rectum into the mantle 

 cavity and its relation to the nervous system may be derived without serious 

 difficulty from a condition similar to that of the Polyplacophora. 



In their broader features the nervous systems of the Solenogastres are all 

 reducible to one type, as Thiele and Nierstrasz maintain. ■ In practically every 

 species described in the present paper, the brain is bilobed and always connects 

 with the pedal, lateral, and labio-buccal systems. In the Neomeniina three 

 pairs of nerves, often associated with small ganglia of problematical homology, 

 are distributed to the anterior end of the body and attach to numerous ganglionic 

 masses applied to the walls of the atrial cavity. In the Chaetodermatina a 

 larger number of nerve bundles arise from the anterior surface of the brain and 

 connect with great ganglionic bodies often almost enveloping the brain. From 

 these ganglia branches pass to the buccal plate. Judging from its innervation 

 the atrial cavity is thus the homologue of the buccal sensory plate (Mundschild), 

 and both are homologous with the Chiton snout. Accordingly the ganglia 

 attached to the brain are the counterpart of those applied to the bases of the 

 cirri. Thiele has called attention to the inappropriateness of the term "buccal" 

 in speaking of these ganglia, and accordingly the term precerebral may he used. 



In a primitive condition the lateral, pedal, and labio-buccal connectives 

 probably arose as independent trunks, but in many species they are more or 

 less fused for some distance. The ventral and pedal ganglia are usually en- 

 larged at the point of union with the connectives, and may originate nerves 

 distributed to the walls of the pedal -gland outlet, atrium and to some extent 

 of the body. Commissures at fairly regular intervals attach the pedal ganglia 

 and may develop small branches distributed to the tissue in the vicinity of the 

 ventral fold or foot. About the same immber of connectives unite the pedal and 

 lateral ganglia, and likewise give rise to small offshoots passing into the somatic 

 musculature. Other nerves, with seemingly the same destination, form from 

 the upper surface of the lateral ganglia and course dorsally. In the posterior 

 end of the body the lateral ganglia usually enlarge and invariably are united 

 by a suprarectal commissure. From these enlargements branches pass to the 

 body and cloacal walls, and from the commissure in the mid line a fibre arises, 

 in some species, that is distributed to the dorso-terminal sense organ. The 

 pedal ganglia may gradually diminish in size posteriorly or become attached 



