406 HAROLD HEATH, 



Comparing the buccal system of the Solenogastres with that of 

 the Chitons fundamental resemblances and ditierences are evident some 

 of which may be accounted for by the concentration of the circum- 

 oesophageal nerve ring and others that do not meet with such a ready 

 solution. Owing to the centralization of the cerebral ganglia the 

 buccal connectives pass backward to surround the pharynx and not 

 forward and then backward as in the Chitons. A dorsal commissure 

 is present in both. In the Chitons it is situated in front of (dorsal to) 

 the buccal cavity and gives rise to two nerves that I have followed 

 (in Cryptochiton stellen) far back on the dorsal aorta and there are 

 indications, noted heretofore, that this is also the case in the Soleno- 

 gastres. The buccal ganglia are usually not clearly defined in the 

 Chitons and when present ordinarily occur at the origin of the dorsal 

 commissure. Up to this point the differences are relatively slight and 

 not sufficient to mask the fundamental resemblances. The greatest 

 disagreement exists in connection with the subradular ganglia and 

 connectives. In the Chitons this system arises from the circumoeso- 

 phageal nerve ring at its junction with the suboesophageal commissure 

 and the buccal connectives ; but here in the Solenogastres it is at- 

 tached far down on the buccal connectives. While it is possible to 

 imagine the method by which this condition of atfairs has been pro- 

 duced it is not possible with the small amount of data at hand to 

 draw any conclusions in which much confidence may be placed. This 

 may only be done after a broad comparative study of many species 

 has been made. 



Commencing at about the level of the seminal receptacle the pedal 

 cords in Proneomenia gradually decrease in size and finally become 

 so delicate that their connections have never been determined. In 

 dissections and in sections also, they have been traced into close 

 proximity to some of the branches from the palliai cords but no 

 actual connection has ever been discovered. The pedal commissures 

 throughout the body proper appear to be about as numerous as the 

 l)allio-pedal connectives. Posteriorly they also become very delicate 

 and finally cease about the middle of the cloacal passage. 



The palliai cords, passing internal to the oviduct, terminate above 

 the cloacal i)assage in the latero-posterior ganglia that are united by 

 a relatively long commissure passing over the rectum (Fig. 6). Exactly 

 in the mid-line a nerve arises from this commissure and passing back- 

 ward terminates in the group of ganglion cells beneath the posterior 

 dorsal sense organ (Figs. 1, 3, 6). None of its branches appear to 



