694 THE REPRODUCTIVE SYSTEM OF DIGASTER, 



body wall. At its posterior end it penetrates the base of the 

 prostate gland and joins the main muscular duct of the latter at 

 the point where it, just formed by the union of several small 

 ducts, is about to enter the body wall. The short conjoint ducts 

 open bv two slit-like pores situated on prominent papillaj on 

 segment xviii. 



In tlie immature specimen already referred to, the vasa 

 deferentia are in an exceedingly interesting condition. The two 

 ducts from the anterior and posterior rosettes of each side, 

 instead of uniting in segment xii., remain distinct tliroughout 

 their entire course. On the one side they appear to join the 

 duct of the prostate separately, while on the other appearances 

 suggest that the two ducts unite before entering the common 

 duct. There are thus present in this young specimen two distinct 

 pairs of vasa deferentia. Whether the single vas deferens of 

 each side in the adult arises through fusion of the two ducts 

 present in the young, or whether one of the two primitive ducts 

 disappears, future investigation must decide. In this connection 

 it is worthy of note that according to Beddai'd* in embryos of 

 Octochcetus there are at first traces of four genital ducts in corres- 

 pondence with the four gonads (there being in those embryos an 

 additional pair of ovaries in segment xii.). 



(b) Sperm reservoii-s. — In segments x. and xi. the anterior and 

 posterior testes and rosettes, together with the ventral nerve 

 cord and the ventral vessel, are enclosed in two medianly situated 

 special compartments of the ccelom functioning as sperm 

 reservoirs. In fig. 1 the right side halves of the reservoirs are 

 shown intact {a.s.r., |:).s.?'.), while on the left they have been 

 opened to expose the contained organs. The cavity of each 

 reservoir is undivided, and contains numbers of developing sperms 

 (fig. 2). 



(c) Seminal vesicles. — Into the reservoirs there open the 

 seminal vesicles or sperm sacs, of which there are two pairs, 

 situated in segments ix. and xii. The anterior vesicles (a.s.s.) are 



* Beddaid, F. E. A Monograph of the Order of Oligochasta, p. 104. 



