88 S. GOTO. 



The above account of spermatogenesis has been based on observa- 

 tions of Microcotyle cauclata ; but the process is essentially the same in 

 all the genera treated of in this paper. It will be seen that it differs 

 in many respects from the statements of other writers '^ on the same 

 subject ; but the various stages observed seem to me to be capable of 

 orderly arrangement only in the way indiaated above. The process of 

 spermatogenesis above described also differs considerably from that 

 which takes place in Diplozoon (PL VI, fig. 4). In this the sperm 

 mother-cell first divides by ordinary mitosis, then effects what has 

 been termed reduction-division ; and each daughter-ceU thus formed 

 developes into a spermatozoon, in which the chromosomes can still be 

 distinctly seen. Finally the mode of division above described is so 

 dififerent from ordinary mitosis that I am not able to say what 

 relation it bears to that. This and other obscure points indicated 

 above I must leave to future investigations. 



Yas deferens — In Tristonntm the vasa efferentia that proceed 

 from the testes can in most cases be traced out ; but this is possible 

 only when they are made visible by' being filled with spermatozoa, 

 which stain very deeply with most colouring fluids. The vasa 

 efferentia unite with one another and finally foi-m a pair of large 

 vasa efferentia, which again unite with each other in the median 

 line of the body and form a single vas deferens. This is at first of 

 small calibre, but becomes gradually larger and larger as it proceeds 

 forwards on the left side of the ovary, and after undergoing numerous 

 smaller windings, forms just in front of the ovary, a large loop, the 

 closed end of which is directed towards the right side of the body, and 

 in most species also more or less forwards (PI. XX, fig. 1 ; PI. XIII, 



1). Kerbert — Beitrag zur Kenntniss der Trematoden. Archiv f. mik. Anatomie, Bd. XIX, 

 1881. p. 559 et infra. Also Monticelli — (According to Braun's report in Ceutralblatt f. 

 Bakteriologie u. Parasitenkunde, XIII. Bd., 1893, p. 180). 



