The nervous system aud .subi'adular organ in two genera of Solenogaütres. 405 



seen leaving the ganglia and appearances indicate that others arise 

 from the adjoining portions of the commissure. All are exceedingly 

 delicate but some may be clearly traced to the base of the subradular 

 organ. 



Rhopalomenia^ as noted previously, is characterized by the great 

 length of the pharynx and buccal system (Fig. 2) and yet the relations 

 of the two are essentially like those of Proneomenia. The buccal 

 ganglia are clearly defined, loosely attached to the pharyngeal wall 

 and are connected by a well developed commissure that lies beneath 

 the pharynx a short distance in front of its union with the stomach- 

 intestine. A very short distance in front of the buccal ganglia the 

 pharyngeal epithelium is of considerably greater height lut the com- 

 ponent cells are not arranged into a sharply marked group that may 

 be defiritely called the subradular organ. It is of much interest, 

 however, to note that immediately beneath this sensory area there is 

 a well defined subradular commissure with two clearly developed 

 ganglia and their connectives, all holding the same relations as in 

 Proneomenia. At the junction of the subradular commissure and each 

 buccal connective is a small group of ganglion cells from which the 

 dorsal commissure (d. c) takes its origin. It is of the same calibre 

 as the subradular commissure and may be traced without great dif- 

 ficulty over the dorsal wall of the pharynx. As the figure shows it 

 is located much nearer the buccal ganglia than in Proneomenia but 

 otherwise shows no striking peculiarities. 



In another species of Solenogastre, whose relationships I have as 

 yet not determined, there is a group of relatively high columnar cells 

 situated in front of the radula but owing to the difficulty of ditieren- 

 tiating the nerves from the dense mat of surrounding muscle and con- 

 nective tissue its homologies are unknown. Several other Solenogastres 

 as figured by various authors also appear to have subradular sensory 

 areas. This is strikingly the case with Proneomenia sluiteri as described 

 by Heuscher^). The drawing of the radula (pi. 27, fig. 13) shows 

 a sharply circumscribed group of very high columnar cells in structure 

 and location almost exactly like one of the subradular organs in the 

 present species of Proneomenia. As nothing is known of the inner- 

 vation of this region in any of these species it is impossible to state 

 that they are subradular organs, yet I have little doubt that at least 

 in Proneomenia sluiteri such is the case. 



1) J. Heuschee, Zur Anatomie und Histologie der Proneomenia 

 sluiteri, in : Jena. Zeitschr. Naturw., V. 27, 1893. 



