G. A. DREW ON YOLDIA LIMATULA, SAY. 17 



through the many sacculated loops already mentioned, the tube again 

 comes near the pericardial wall, enlarges, runs alongside the anterior 

 turn of the inner end, narrows down again and opens into the mantle- 

 chamber through an antero-posteriorly elongated opening, mco., just 

 posterior to the point where the outer and inner ends of the tube cross. 



The genital duct, gd, following the course of the cerebro-visceral 

 commissure, turns ventrally when almost in contact with the inner end 

 of the excretory organ, meets the outer end, and opens with it. The 

 common opening of the excretory organ and genital duct is, as has been 

 noticed, elongated in an antero-posterior direction, Fig. 23, mco., and 

 may represent a fusion of the two rather than an opening of one into 

 the other. 



As has been seen, the condition described by Pelseneer, 11 viz: the 

 genital duct opening into the excretory organ near its pericardial 

 opening, is not borne out by these observations. 



In material that is not well preserved it not unfrequently happens 

 that the walls of the genital duct and the inner end of the excretory 

 organ are ruptured in sectioning, at the point where they come in 

 contact, thus placing their cavities in communication. 



It may be well to state in passing that the genital ducts of Nucula 

 proxima open into, or with, the outer end of the excretory organs, in a 

 manner similar to that just described for Yoldia limatula. 



GENITAL GLANDS. 



These, when distended with their products, are very extensive. 

 They push in between the excretory organs, below the pericardium, 

 between the stomach and intestine nearly to the pedal ganglia, and 

 cover and dip in between the lobes of the digestive glands. The opening 

 of the genital duct, Fig. 23, gd, has already been described in connection 

 with the excretory organ. 



The sexes are separate and, when the genital products are abundant, 

 they may easily be distinguished by the color of the genital mass 

 surrounding the digestive glands. This portion is chocolate brown in 

 females and yellow in males. 



NERVOUS SYSTEM. 

 FIGURES 4 AND 5. 



The cerebral ganglia, Fig. 4, eg, united in front of the oesophagus 

 by a very broad commissure, which differs very little in structure from 



