CHAPTER m 

 DEVELOPMENT OF MONOGENETIC TREMATODES 



As was indicated, the formation of eggs takes place in the o'dtype p. 86 

 and the speed of their formation can sometimes be considerable. Thus, 

 according to our observations, the time during which an egg is formed among 

 Dactylogyrus vastator Nybelin fluctuates from 4 to 20 minutes, whereas 

 among Polystoma integerrimum Froelich this period is sometimes decreased 

 to one and one half minutes. The number of eggs deposited by a single indi- 

 vidual monogenetic trematode is very great; this is true in equal measure of 

 the species with short life spans as well as those with long. ones. Thus, among a 

 number of species of Dactylogyrus the egg deposition continues almost the 

 entire summer, and it is more or less uniform during this time. Very 

 interesting are observations in the deposition of eggs of D. vastator which 

 were conducted by N. A. Izumova. According to her very meticulously 

 executed experiments, it was foiond that in surroundings which approach natural 

 conditions^ vastator deposits eggs very intensively but not uniformly de- 

 pending upon the age and the oxygen conditions of the milieu. Generally, we 

 can expect that at normal oxygen levels worms which begin laying at the age 

 of eight days after attraction to the host deposit from 4 to 10 eggs in a period 

 of 24 hours at 12° to 18° C during the first ten days. A decrease in oxygen 

 and a rise in the water temperature result in an increase in the number of 

 eggs deposited. That is why it is so easy to acquire an intensive laying of 

 D. vastator in artificial and obviously unfavorable conditions. 



Among Polystoma integerrimum Froelich, according to our 

 observations in natural conditions, the eggs deposited during the spring egg- 

 laying period reach 2,000 to 2,500 and on separate days the number fluctu- 

 ates from a few to 1500. As observations indicate, certain individuals of 

 P. integerrimum p roduce eggs more or less uniformly through a number of 

 days, and others deposit at first a large number of eggs and then their laying 

 is quickly curtailed and then completely stops. It is apparent from Table 1 

 which way the process takes place among different individuals which are 

 found in the host singly and among several parasitizing the frog at the 

 same time. The egg-layings, the data concerning which are given in the table, 

 took place under experimental conditions at an earlier time than in nature, 

 but their nature fully corresponds to this process under natural environ- 



mental conditions. 



The process of egg formation among monogenetic trematodes can 

 be considered as almost completely unstudied. During the observations of 

 development of eggs among Dactylogyrus we often"had eggs with already 

 formed but still soft shells containing onlyihe egg cell. These eggs had 

 open posterior ends and into them were poured, after a certain time, vite- 

 lline cells and this infusion was accompanied by intense contractions of the p. 87 



85 



