of tJie Bay of Naples. 99 



tuous ducts {v.d.) as vasa deferentia which conduct the semen 

 into the great cavity of the ductus ejaculatorius {d. ej.) . Per- 

 haps, indeed, there is only one vas deferens which possesses 

 two anterior apertures. 



The testes are often very difficult to find, especially when 

 they lie immediately above the brown stomach. They are 

 clothed with a delicate membrane, which contains in its inte- 

 rior many small cells, and in the mature state numerous 

 active and very small spermatozoa. In each of the latter a 

 head and a caudal thread may be easily recognized. In the 

 testes of the freshwater Rotatoria, as is well known, besides 

 the true spermatozoa, which resemble those just described, we 

 find motionless bacilli, pointed at the two ends, of which the 

 nature is doubtful. I have generally missed these in Para- 

 seiso7i, and only once observed an aggregation of bacilli (?/) 

 which might represent those just described. The seminal 

 vesicle is filled with a finely granular mass, probably con- 

 sisting of densely-packed spermatozoa. 



The contents of the other parts of the generative apparatus 

 are very remarkable. The ductus ejaculatorius contains a 

 great number of flask-shaped corpuscles (figs. 11, 12, 13), 

 averaging 0"014 millim. in length and O'OOo millim. in 

 breadth, which are themselves incapable of motion, but of 

 which some are not unfrequently driven by ciliary action into 

 the vasa deferentia. In each flask we can distinguish three 

 divisions, namely an anterior hemispherical cap (fig. 12, a), a 

 somewhat narrower neck (b), and an ovate hinder portion (c), 

 which is two or three times the breadth of the neck. Tlie 

 anterior and middle parts are clothed with a thin chitinous 

 membrane, whilst the capsule of the last division is thick and 

 firm. These conditions are best recognized by allowing a 

 drop of solution of potash to act for a short time (fig. 11). 

 We then see that the dark shining rod, which traverses the 

 whole length of the neck, is not a canal, but a solid structure, 

 which projects somewhat into the anterior and posterior 

 pieces. The remainder of the neck is either without contents 

 or occupied by a limpid fluid. In the anterior division of the 

 structure under consideration there is a granular protoplas- 

 matic substance, which looks as if it consisted of a dense 

 accumulation of spermatozoa. It is wanting in the imme- 

 diate vicinity of the anterior end of the neck-axis, so that, as 

 shown in fig. 12, it arches over this central rod like a hood j 

 only a fine streaking is to be recognized in tlie clear space 

 between the neck and the plasma. Whether the latter really 

 consists, as I believe, of a closely entwined coil of seminal 

 filaments I could not decide with certainty ; no movements 



