1 



Indications to the effect that at the time of deposition, P^ integerrimum 

 extends outside from the cloaca are not substantiated by our observations. 



The shortening of the period of formation and deposition of eggs 

 creates a necessity of a large number of morphophysiological peculiarities 

 in the functioning of the sex system. As we saw in the example of P. 

 integerrimum from the urinary bladder, the yearly cycle of the sex system 

 is completely subjugated to this problem and the processes of oogenesis and 

 spermatogenesis, of the formation of vitelline food cells, the production of 

 all auxiliary glands becomes strictly cyclical and takes place in such a 

 fashion as to make possible the maximal use of all sex products which are 

 available in the shortest period of the egg -laying. This is especially 

 noticeable in comparing the characteristics of action of the sex system and 

 the morphological peculiarities in both forms of P. integerrimum . We will 

 note once more that "gill" P. integerrimum with an extended (although rela- 

 tively short in time) period of the action of the sex system do not have a 

 uterus but only an ootype, they have a different form of the ovary connected 

 with a gradual ripening and expenditure of egg cells, and they have no vaginal 

 ducts, etc. The differences in the deposition of eggs of both forms are 

 closely related to the peculiarities of life and location of the stages of 

 development of frogs infected by them. P. integerrimum from the urinary 

 bladder has the opportunity of depositing eggs vmder conditions favorable to 

 the subsequent development of the larvae only during the short period of 

 the presence of the frogs in the body of the water at the time of their spawn- p. 130 

 ing because at another period the frogs are located in a different medium 

 of habitat, and the eggs of the parasite deposited at the time are inevitably 

 condemned to death. The gill form of P. integerrimum parasitizes tadpoles 

 for its entire life and perisheswith their metamorphosis, consequently eggs 

 deposited by it during the entire period of egg -laying fall into the medium 

 favorable for the development and, as we saw before, have considerable 

 chances for infecting the host. Along with the changes in the structure and 

 functioning of the sex system, a number of adaptations toward peculiarities 

 of life cycle is reflected in the structure of the eggs and also in the place 

 of their location after deposition, as was previously mentioned. The re- 

 tention of eggs on the body of the host is an important adaptation among 

 many forms parasitizing fishes which lead a gregarious form of life and 

 which perform considerable migrations. Among parasites of such fishes, 

 it gives the same result as rationed egg -laying, as was already noted. 

 However, here we encounter the substantial question of cross -infection 

 of the fishes for without the latter the probability of the flourishing of the 

 parasites as a species would have been extremely small. Increased in- 

 fection of the same individual of host by newer and newer individuals would 

 have worsened the conditions of existence of the host and by that very fact 

 would have influenced negatively the condition of the existence of the parasite 



136 



