1916.] NATURAL SCIENCES OF PHILADELPHIA. 479 



THE NERVOUS SYSTEM OF CREPIDULA. ADUNCA AND ITS DEVELOPMENT. 



BY HAROLD HEATH. 



The genus Crepiduh in the vicinity of Monterey Bay, California, 

 is abundantly represented by the members of two species, C. adunca 

 and C. nivea. In each case the young are retained in capsules within 

 the mantle cavity of the parent, and are liberated when they have 

 attained the form of the adult and are in possession of all the definitive 

 organs with the exception of those belonging to the reproductive 

 system. It is accordingly readily possible to secure extensive series 

 of embryos and to follow the course of development from the ovum 

 to the adult. The embryology of several species of this genus has 

 been studied in great detail by Conklin ('97), 1 and as a result it is 

 clearly established that they all pursue essentially the same develop- 

 mental path until they reach the veliger stage or a corresponding 

 point where a free-swimming larva is lacking. Beyond this point 

 nothing is known. 



In connection with a comparative study of the nervous system of 

 several families of mollusks, I have examined adults of the two 

 above-mentioned species of Crepiduh. with considerable care and 

 have traced its development in C. adunca. In view of the fact that 

 Paludina vivipara as worked out by Erlanger ('92) 2 is the only other 

 gastropod whose development in this respect is known, the results 

 possess an enhanced degree of interest. 



The central nervous system of the adult C. adunca is located in 

 the base of the neck, in a spongy mass of connective tissue, placed 

 between the pedal musculature and the overlying mantle cavity. 

 It conforms to the highly centralized type characteristic of the 

 monotocardia generally, with cerebral, pleural and pedal ganglia 

 closely appressed. In several instances, especially in half-grown 

 individuals, the line of demarcation between the cerebral and pleural 

 ganglia is comparatively slight; on the other hand, the pedal ganglia 

 are invariably sharply defined. All are globular bodies of essentially 

 the same size and, as indicated previously, are united by compara- 

 tively short commissures and connectives. 



1 The Embryology of Crepidula, ./nun*. Morph., Vol. 13. 1897 



2 Zur Entwickhm^ von Paludina vivipara, Morph. Jahrb., Vol. 17. l v 



