SEA MUSSEL MYTILUS EDUUS. 



I8 3 



In both sexes the follicles are lined with germinal epithelium, the minor genital 

 ducts are bordered with germinal epithelium on one side and ciliated epithelium on the 

 other (fig. 177, p. 184), and the main canals have their walls thrown into longitudinal 

 ridges which are covered entirely with columnar ciliated epithelium. They are sur- 

 rounded by a thin layer of fine muscle fibers which increase in number toward the 

 genital orifice. The opening on the papilla has two distinct lips which may completely 

 close it when they are brought together by muscular action (fig. 162, GO, p. 173). 



.-/' 



174 



Fig. 174.— Terminal branches of a minor genital canal in a male mussel showing follicles which are lined internally with 

 germinal epithelium and filled with genital products. X as.' Drawing made from a total preparation which was fixed in Gilson 

 fluid, stained with borax -carmine, dehydrated in alcohol and cleared in oil of wintergrecn. /•". follicles; GC, a minor genital 

 canal. 



Fig. 17s.— Branching genital canals and follicles in a female mussel. X 23-8.' Preparation same as fig. 174. F, follicles. 

 smaller ones with transparent walls showing ova contained within; GC. minor genital canals also filled with ova. 



The ova and spermatozoa arise from the germinal epithelium lining the follicles and 

 minor genital canals. Before the germ cells begin to grow the epithelium is membranous 

 in character and composed of very small cells. As the ova develop, their area of attach- 

 ment increases greatly in thickness (fig. 177, GE, p. 184). Their nuclei are very promi- 

 nent, containing large, conspicuous nucleoli, and are surrounded by a thin layer of 



3 The relative sizes of the follicles shown in figures 174 and 17s. according to the magnifications given in the legends, do not 

 correspond with the description in the text and suggest that a mistake was made in the figures given for the magnification of 

 either figure 174 or 175, or both. 



