STRUCTURE OP THE NEPHRIDIA OF DINOPHILUS. 539 



figure he states, p. 14, '^ the vesiculse seminales were in their 

 definitive position in the fifth body segment, and their iden- 

 tification as vesiculte was rendered sufficiently certain by 

 the fact that they contained ripe spermatozoa. The vesiculae 

 were arranged in an obliquely transverse position, their 

 outer portions ending blindly at the level between the two 

 ciliated rings of the fifth segment, their inner ends opening 

 into the cavity of the testis. A part of the vesicula imme- 

 diately succeeding the internal aperture was lined with long 

 cilia; the next part of the tube contained a small mass of 

 spermatozoa. The penis was well developed, and obscure 

 indications of a duct leading from the vesicula to the penis 

 was observed ; the existence of the duct was not, however, 

 completely proved. The resemblance of the young vesicula 

 seminalis to an ordinary nephridium was manifest not only in 

 its shape and position, but still more conspicuously by the 

 fact that its walls contained an orange pigment, exactly 

 resembling that so commonly found in the walls of the 

 excretory tubes." 



Numerous stages between this form and the mature con- 

 dition were observed. " The final form is acquired by the 

 gradual distension of the originally subcylindrical tube by 

 spermatozoa, this distension being accompanied by an altera- 

 tion in the direction of its axis, the result of which process 

 is that the end which, in the young vesicula, is external, 

 is situated in the adult condition in front, the whole organ 

 having now acquired an antero-posterior direction. The 

 funnel during the above changes will naturally come to be 

 situated near the posterior end of the organ." '' It must be 

 especially noted that the funnel of the vesicula is in a posi- 

 tion corresponding with that of the ciliated appendage of an 

 ordinary nephi'idium, and that the original external aperture 

 of the modified nephridium was probably (in the phylo- 

 genetic history of the organ) at the opposite end of the tube, 

 which ultimately becomes the blind anterior end of the 

 vesicula. The relations of the outer ends of the young 

 vesicula to the ciliated rings of the fifth segment further 



