1 82 BULLETIN OF THE BUREAU OF FISHERIES. 



REPRODUCTIVE SYSTEM. 



ANATOMY. 



The reproductive system consists of numerous ducts which branch throughout 

 nearly the entire body, giving off in turn smaller branches which terminate in pockets or 

 follicles. The greater part of the system occupies the mantle lobes, which are filled 

 almost exclusively with reproductive tissue just prior to spawning. It also fills the 

 mesosoma, penetrates through the tissues just below the pericardial chamber, lines the 

 walls of the lateral cavities, and spreads over the outer surface of the liver. Practically 

 every part of the body with the exception of the gills, muscles, and foot is covered or 

 occupied by the genital organs. This is well shown by a cross section taken through the 

 middle of the body of a mussel i year old which was about to spawn for the first time. 

 (See fig. 147, opp. p. 163.) 



The main genital ducts lie near the outer surface of the mantle lobes and converge 

 to a point of common union which lies just below the pericardium. In general there are 

 five principal canals which meet at this point: (1) A main branch which supplies the 

 anterior region of the mantle and the surface of the liver, (2) and (3) two lateral branches 

 which supply the mid region of the mantle, (4) a posterior branch which connects with 

 the hinder parts of the mantle, and (5) a dorsal branch which supplies the area between 

 the posterior adductor muscle and afferent oblique vein and the dorsal body wall (fig. 

 162, GC, p. 173). 



From the point of union of these several ducts, the main genital canal thus formed 

 on each side of the body penetrates the mantle to its inner surface, where it turns back- 

 ward and runs on the ventral body wall just inside and parallel with the attached edge 

 of the inner gills to the genital papilla on which it opens to the exterior. The genital 

 papilla lies a short distance in front of the posterior adductor muscle in the angle formed 

 at the base of the mesosoma with the inner gill. A median branch from the common 

 genital canal connects with the mesosoma on each side of the body. 



HISTOLOGY. 



If the mantle of a mussel which has almost finished spawning is treated with Gilson's 

 fluid or some other suitable fixing solution and then stained with borax-carmine, dehy- 

 drated, and cleared, preferably in oil of wintergreen, the minor canals and the follicles 

 connected with them can be seen easily under the microscope when examined with low- 

 power lenses. 



In male animals, the follicles are small outgrowths from the sides of the canals. 

 They are of almost uniform size, very numerous, and situated about the same distance 

 apart (fig. 174). 



In the female the arrangement of the canals is the same as in the opposite sex, but 

 the follicles are larger, much less numerous, and more variable in size. 2 In some cases 

 they appear to be lateral outgrowths of the genital canals, while in others thev form the 

 blind ends of the ducts (fig. 175). 



J 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 17s, or both. 



