ASPIDOG ASTER CONCHICOLA. 



175 



primary ona^ as they may be termed, become detached, and 

 pass into the oviduct. Here they are fecundated, and, be- 

 coming surrounded by a great mass of accessory yelk, and a 

 shell, gradually acquire the appearance of the complete ova. 



The accessory yelk is the product of the vitellarium — a 

 large double gland consisting of a number of oval, pyriform, 

 or irregular granular masses placed on each side, at the junc- 

 tion of the sucker with the body (Fig. 40, g). 



These masses appear to be quite independent of one an- 

 other ; nor do they at first present any obvious communication 

 with the genitalia ; but if the oviduct, just after it becomes 

 free from the ovarium, be examined, it will be found to re- 

 ceive a short duct (Fig. 42,/), filled with strongly retracting 

 granules of the same nature as those in the vitellarium. This 

 duct is enlarged posteriorly, and then divides into two ducts 

 filled with the same matter, which take a direction toward the 

 vitellarium, but can be traced no further than they contain 

 granules (Fig. 42). By the careful application of pressure, 

 however, the granules may be forced from the vitellarium, 

 through an anterior and posterior branch upon each side, into 

 these ducts. 



Fig. 4^.—Aspidof/aMer conchicoIa.—Reipro^nctive orsans on a larger scale. Letters 

 a?: in Fi<r. 40. The commencement of the external vas deferens^is seen behind the 

 vitellarian ducts. 



The oviduct (Fig. 42, i) is richly ciliated internally ; it is 

 at first applied to the under surface of the ovarium, and when 

 it becomes free it receives a canal (e), which may be traced 



