CHAETODERMA HAWATIENSIS. 53 



This part of the nervous system is thus essentially as we find it in other 

 Solenogastres. In Proneomenia hawaiiensis, for example, the supraoesophageal 

 ganglia are connected with several nerves some of which unite with groups of 

 ganglion cells attached to the bases of the cirri, and from these again other nerves 

 pass to the digestive tract and probably to the body wall. In Chaetoderma the 

 chief difference is that the nerves uniting the brain and precerebral ganglia are 

 very short. 



In the present species the pedal and lateral connectives unite immediately 

 before plunging through the precerebral ganglia, and as Plate 7, fig. 2 shows the 

 labio-buccal cord unites with them before the brain is reached. This same 

 condition of affairs exists also in two species of this genus taken in Alaska, though 

 much more obscured than in the present species. At the posterior end of the 

 prothorax the pedal and lateral cords that have gradually approached each other 

 actually come in contact and in one specimen even fuse for a short distance and 

 lose the usual sheath of ganglion cells. Anterior to this point two pedal com- 

 missures exist, but until the hindmost part of the body is reached no farther 

 trace of such nerves has been found. On the other hand latero-pedal connectives 

 are present throughout the entire length of the animal. 



The relations of the labio-buccal ganglia are represented in Plate 7, fig. 2. 

 The non-ganglionic connectives imbedded in the pharyngeal wall unite with 

 the superficially attached ganglia, that are also united by a conmiissure passing 

 behind the median tooth. In front of the radula there are connectives giving 

 rise to nerves passing dorsally to what is probably the subradular organ and in 

 addition attaching to a ganglionic mass in the mid line. As this part of the 

 nervous system appears with greater distinctness in C. attenuala it is more fully 

 described in that connection. 



Throughout the entire metathorax the lateral and pedal cords pursue their 

 course almost in contact, here and there giving rise to nerves that soon disappear, 

 and finally join in the extreme posterior end of the body. Shortly after their 

 imion they are connected by a heavy ganglionic commissure passing dorsal to 

 the intestine. In the mid line it develops a single nerve that makes its way into 

 the tissue of the rectum, while on the dorsal side four fibres originate, two of 

 which pass at once into the gills while the others attach to the inner side of the 

 cloacal epithelium, and branching repeatedly supply this membrane and the 

 dorsal body wall and a well-marked fold of the hypodermis to be described 

 presently. At the junction of the latero-pedal cord and the commissure a nerve 

 arises that passes backward and appears to supply the ventral body wall of the 

 cloacal region. 



