stickelbacks) and others on solitary fishes (G. groenlandicus Levinsen 

 from gobies). All this taken together means that the question concerning 

 life cycles of different Gyrodactylua deserves special studies and probably 

 will yield much that is new and interesting. 



In connection with the problem of life cycles^ one must pause 

 to examine certain aspects of the question of dynamics of numbers of 

 monogenetic trematodes. As we have already indicated (pageg'O), this 

 question has great practical significance in addition to the theoretical one. 

 First of all let us analyze the peculiarities of accretion in numbers under 

 ideal conditions for egg -depositing and viviparous forms. As examples 

 for the analysis of the given phenomena it is convenient to use the material 

 on Dactylogyrus vastator Nybelin and Gyrodactylus elegans Nordmann from 

 Carp. We shall attempt to show in which fashion the numbers must accrue 

 among both types, on the condition that all the larval Dactylogyrus emerging 

 from the eggs, or correspondingly all the individuals of Gyrodactylus which 

 are born, survive and continue their normal existence until natural death 

 from old age. It is understandable that this almost never occurs in nature, 

 but such a theoretical calculation will give us much that is essential for 

 the understanding of relations between both types of reproduction. For the 

 estimate of the reproduction of D. vastator we take the following data (see 

 P^g^ 108 )'■ the period of development of eggs--three days, development of 

 larvae until maturity and first deposition of eggs --6 days, the span of life 

 from the moment of nnaturity- - 12 days, the number of eggs deposited daily-- 

 5; for G. elegans (see page 131 ): the development of eggs in the uterus 

 until the emergence of the first daughter individual- -4 days, the emergence 

 of "remaining" embryos in sequence a day after the birth of the correspond- 

 ing worm, the span of life of the worm from 13 to 14 days depending on the 

 presence or absence of "remaining" embryos. Of course, all these periods 

 are inexact and can have only an orienting oignificanceJ'or practical purposes 

 the calculation of the accretion of numbers of both types within the limits 

 of one month is interesting because this is the usual period of crowding of 

 the yovmg fishes in the spawning ponds where greatest infection is possible 

 and where occurrences of epizootics are even observed. The common scheme 

 of accretion of the progeny from one individual D. vastator and G^ elegans 

 is represented in Figs. 132 and 133. They are compared in such a way as 

 to make the general character of changes apparent. Unfortunately, technical 

 difficulties permitted us to represent the process for only 20 days. As for 

 the remaining period the development of changes is expressed in curves of 

 the accretion of numbers (Fig. 134 and Table 2). 



From these data it is apparent that the resulting figures of the 

 changes in numbers of both types obtained almost coincide basically in spite 

 of the connpletely different means of reproduction. Moreover, Gyrodactylus 

 yields a greater number of progeny during the first period (up to 20 days) 

 than Dactylogyrus . The first interesting deduction from this is that vivipa- 

 rous Gyrodactylus potentially possess a very high tempo of reproduction 



142 



