interrupts it for a more or less prolonged period. As regards morpho- 

 logical differences between the "winter" and "summer" eggs one should 

 consider them as nonexistent, or more precisely that the observed facts 

 were not correctly interpreted. According to our observations and also 

 according to the data of Kulwiec (Kulwiec, 1929), the same specim.en of 

 D. vastator deposits, at any time, eggs which vary extremely in size so 

 that some could be considered as "summer" and some as "winter. " How- 

 ever, their further development is completely uniform and no difference 

 is observed in periods of development. It is clear from these reproduced 

 data that in the spring infection can take place from hibernating eggs, but 

 there is no basis for acceptance of the hypothesis of "winter" eggs to 

 explain this. The existence of adult individuals in the winter periods, 

 which is denied by a number of authors, is actually indisputable. Thus, 

 as early as 1929 during our student work on the trematodes of the fishes 

 of the Volga River in the vicinity of Kostroma, we succeeded in showing 

 that all the species of Dactylogyrus occur in the coldest months of winter on the 

 most diversified fishes. An unusually low quantity of parasites and also a 

 severe lowering of the percentage of infection of separate fishes constitutes 

 a peculiarity of winter infection. All subsequent studies substantiated the 

 given conditions. Thus, A. P, Markevich found Dactylogyrus and even their 

 eggs in January and February on the gills of Carp in the Nikolsk fish farm 

 (Markevich, 1934). In the work of E. M. Lyman (1951b) are reproduced 

 data concerning the infection of Carp during the winter by gill trematodes 

 D. vastator and D. anchoratus (Dujardin) in which it is clear that for D. 

 anchoratus the percentage of infection remains very high during the entire p. 108 



winter, whereas for D. vastator both the percentage of infection and the 

 quantity of the parasites are lowered. From the work of Lyman it is also 

 apparent that he also observed egg-laying by D. vastator during the winter. 

 This appears to us erroneous. It is more probable that Lyman dealt with 

 individuals which began depositing eggs after the transfer of infected fishes 

 into the laboratory, that is during the changed temperature regime. 



Under natural conditions, the life span of D^ vastator, as has been 

 pointed out in Chapter 2, fluctuates very much, but in summertime it is not 

 less than 20 to 25 days in spite of the opinion of Groben (Groben, 1940)^ who 

 believes that D. vastator lives only 10 to 12 days (including the embryonic 

 development). The individuals infecting fish in the late autumnal period 

 partly perish during the lowering of temperature and partly hibernate. In 

 such a fashion the life span of the latter can reach 6 7 months. The life 

 of the separate individual from the moment of emergence of the larva from 

 the egg consists of several hours of existence in the free -swimming stage 

 and then a period extending from the moment of the settling of the larva on 

 the gills of the host lantil maturity, a period which among D. vastator under 

 conditions of the Leningrad region, i.e., at summer water temperatures 

 about 14 to 17°, continues for 6 to 8 days, and the interval of time from 

 the beginning of maturity until death, which extends not less than 12 days. 

 The deposition of eggs takes place during the entire life of the worms but 



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