region of his research, this seems improbable to us because the frogs 

 never (rarely?, nobis) are found at the places of deposition of the eggs 

 fifteen days before spawning, and this possibility takes place in certain p. 128 



exceptional cases but not as a rule. Hence, his data concerning the 

 development of the eggs in nature during 40 to 50 days also seem improbable 

 to us. The same also can be said concerning the data of Zeller. The 

 second basic difference between our and Gallien's material is that the 

 gill forms produce eggs which, according to our data in the main produce 

 larvae capable of infecting tadpoles, whereas according to Gallien a large 

 part of them develop practically as "non-breeders" because the larvae 

 which emerge have no chance whatsoever of infecting tadpoles. Thus, in 

 the Leningrad region the gill forms develop during the first 20 to 25 days 

 of June, whereas in France, according to Gallien, during only 10 days in 

 the middle of May. In connection with these peculiarities of the develop- 

 ment of tadpoles, the gill form.s lay eggs in our region in about 50 days, 

 but in France in about 35 days. As a result, the larvae emerging fronn the 

 eggs of "gill" P. integerrimum in the Leningrad region succeed in infecting 

 tadpoles for 50 days and perish during the last 5 days at a maximum, where- 

 as in France the emergence of the larvae takes place during 35 days and the 

 infection of the tadpoles--the first 20 days and not 15, i. e. , 43 per cent of 

 the time the larvae do not find hosts for themselves and perish. It seems 

 to us that these data of Gallien demand re -examination- -we think that here 

 are certain inaccuracies of observations. As is clearly seen from the 

 attached diagrams (Figs. 129 and 130), all the rest agrees fairly well and shows striking 

 lation of cycles of the host and the parasite in different geographical locations. 



Before passing to certain general considerations about the life 

 cycles of egg laying of monogenetic trematodes we do not think it would be 

 out of place to cite an example of a break in the link between the biology of 

 tadpoles and P integerrimum which we observed in 1929. In one of the 

 ponds of the Sacred (Forbidden, nobis ) Park of Peterhof of the Institute of 

 Natural History, the deposition of frog roe and of ^ integerrimum took 

 place near the south bank. Because of the land breeze, the main mass of 

 tadpoles which had just emerged from the roe found themselves at a distance 

 of 2 to 3 meters from the place of spawning. As a result though 100 

 per cent of the tadpoles which remained (in place, nobis ) were infected by 

 P. integerrimum, 100 per cent of the tadpoles which were found to the side 

 were uninfected. Thus, a circumstance which may at first glance appear 

 insignificant, such as a distance of from 2 to 3 nneters, did not permiit the 

 union of the links of the chain of the life cycle of the parasite. 



Summarizing our information about life cycles of egg -laying 

 forms of monogenetic trematodes, we must note first of all their increased 

 adaptability to the cycles of the host. Even in the simplest cases, a number 

 of peculiarities are apparent which point to the very long period of the working 

 out of the adaptations of the parasite to the peculiarities of 

 the life cycle of the host, and this under the completely determined conditions 



134 



