Cross -fertilization without the help of copulation (this method 

 was first indicated for digenetic trematodes by Sinitsin in 1906) can take 



place among certain speciesliving in the regions of low concentration and 

 their spermatozoids are ejected from the copulatory organs of one indi- 

 vidual of the parasite and reach the sex glands of the other through the 

 surrounding medium. In addition to that, there is reason to believe that 

 a number of species form spermatophores (apparently many Dactylogyridae, 

 and apparently a number of highest species). 



Self-fertilization among Monogenoidea occurs very often 

 in all families. It takes place either by means of self -copulation (this, 

 however, is subject to doubt), or without copulation by means of cross- 

 fertilization through the surrounding medium. Certain species are mainly 

 self-fertilizing (for instance Dactylogyrus iwanowi Bychowsky), while a 

 large majority has recourse to this method only where cross -fertilization 

 is impossible. Thus for instance during the presence of one parasite in 

 the urinary bladder of the frog (and this can be almost in 50 per cent of the 

 cases of infection Polystoma integer rimum Froelich), the copulation which 

 we just described fertilizes itself, and no delay in egg -laying or abnormal 

 development of eggs has been noticed. 



The adaptation to cross -fertilization among Diplozoon paradoxum 

 Nordmann is completely different. The adult forms of this species are 

 encountered only grown in pairs in a criss-cross fashion. In them the ducts 

 of the female sex system of each individual grows together with the ducts of 

 the male sex system of the other so that for the entire life the possibility of 

 cross -fertilization is insured and conversely self-fertilization is excluded 

 (Zeller, 1872b). The same peculiarity is possessed by other species of 

 the genus Diplozoon. Apparently, nevertheless, cross -fertilization occurs 

 nnuch more often than one can suppose and, of course, than can be observed. 

 It can be guaranteed by the alternate ripening and development of male and 

 female sex products, which was observed by a number of authors. Thus, 

 Sproston, (Sproston, 1945b) saw this among Octostoma scombri (Kuhn). 

 She considers that among the worms there are at least three phases during 

 their lives when the male systemi acts predominantly and two when the 

 fennale predominates. As a rule the male system begins to function first; 

 our data also substantiate this. 



The functioning of the female sex system falls into a number of p. 84 

 successive phases. Thus the activity of its separate parts takes place, now 

 during the time of the reproductive period, now beyond it, and finally in both. 

 As an example of the activity of the female sex system we shall analyze it 

 among Polystoma integerrimum, a specie which was especially studied by us 

 for a number of years. Everything that will be said further about this can 

 be extended to the rennaining Monogenoidea, with the exception that among 

 specieswith an extended period of laying these stages can coincide in time 

 and part of them, specific for Polystoma, is completely excluded. 



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