504 



Genital Glands. 



The sexes are separate, and the genital glands are very exten- 

 sive. In Yoldia, at least, the sexes may be distinguished by the color 

 of the genital organs surrounding the digestive glands. This portion 

 is chocolate brown in females, and yellow in males. The openings of 

 the genital ducts have been described in connection with the excretory 

 organs. 



Nervous System. 



The two species of Nucula seem to differ from Yoldia, in having 

 a distinctly double origin for each cerebro-pedal commissure. In all, 

 the cerebro - visceral commissures are very large and contain many 

 nuclei near their surfaces. The cerebro-pedal commissures show ordi- 

 nary structure. All of the ganglia are rather large. The visceral 

 ganglia of Yoldia are placed close together, while in Nucula they are 

 widely separated. 



Otocysts. 



The otocysts are rather large, and their epithelial cells carry 

 rather long and slender cilia. As shown by Pelseneer (7), there is, 

 in adult specimens, a well defined canal connected with each otocyst. 

 In both species of Nucula this canal opens on the surface of the foot *). 

 In Y. limatula I have never been able to trace the otocystic canals 

 near the surface of the foot. 



By careful dissection of specimens of Yoldia preserved in for- 

 maline, the cerebro-pedal commissures, with the otocysts, otocystic 

 canals, and otocystic nerves, all held together by connective tissue, 

 can be removed. 



Fig. 7. Otocyst of Yoldia limatula. cpc cerebro-pedal commissure, oc otocystic 

 canal, ol otolith, on otocystic nerve, op otocystic pouch, ot otocyst. 



Study of these preparations, of which I have made nearly thirty, 

 show the canals, Fig. 7 oc, to be cylindrical, and of a uniform size 

 for about three-fourths the length of the otocystic nerves, ow, at which 



1) In N. proxima I have not demonstrated the lumen of the canal 

 for its whole length. 



