365 



Nachdruck verboten. 



The Solenogastre Subradular Nerrous System. 



By Harold Heath, Leland Stanford Jr. University, California. 



With one figure. 



In the solenogastres the nervous system is probably the most 

 interesting since it is the most conservative, retaining many ancestral 

 features indicating relationships otherwise most obscure. For many 

 years its main elements and their relations have been known, but 

 several details, some of them of the highest importance in the study 

 of molluscan phylogeny, remain enigmatical. Among these is the so- 

 called buccal or stomatogastric system, consisting of a connective arising 

 from the brain on each side and passing backward to a ganglion 

 (Fig. 1 h) imbedded in the pharyngeal musculature. The ganglia in 



Fig. 1. Diagram of the labio- 

 buccal and subradular nervous system 

 in the genus Chaetoderma, ventral 

 view. The amount of fusion of the 

 connectives arising from the brain 

 varies with the species. Ventral com- 

 missures and connectives not shown. 

 b labio-buccal ganglion. I lateral gan- 

 glion, o nerve to subradular organ. 

 r radula. s subradular ganglion. 

 V ventral ganglion. 



turn are united by a commissure passing beneath the gut in the 



neighborhood of the radula or the outlets of the ventral salivary glands, 



A few years ago i) I discovered a subradular organ in Proneomenia 



hawaiiensis (similar in character to the one figured by Heuscher ^) in 



1) H. Heath, The Nervous System and Subradular Organ in two 

 Genera of Solenogastres, in: Zool. Jahrb., Abt. f. Anat., Bd. 20, 1904. 



2) G. Heuscher, Zur Anatomie und Histologie der Proneomenia 

 ! sluiteri, in: Jen. Zeitschr. f. Naturw., Bd. 27, N. F. Bd. 20, 1892. 



