of the existence of the latter. The peculiarities of the cycle of Monogenoidea 

 find a considerable reflection in various adaptations which arise at first in 

 the sex cycle of the animals, and also in the annual cycle of development. 

 First of all, without any doubt, common historical orientation in the develop- 

 ment of peculiarities of action in the sex system proceeds along the line of 

 the gradual transition from an extended period of egg-laying to its con- 

 traction (shortening, nob is) to a greater and greater degree, which we ob- 

 serve among the fresh water as well as among the migratory and purely 

 marine forms. This is especially evident among the parasites of the 

 Amphibia, i. e., hosts which change their means of habitat from the water 

 to the land during their life span. The reasons for this historical process, p. 129 

 which takes place with various degrees of intensity among various groups, 

 are undoubtedly caused by the necessity for creation of more favorable 

 conditions for the infection of hosts. At first sight, the presence of an 

 extended period of egg-laying appears to be more favorable under con- 

 ditions of continuous (not apportioned, nobis) egg production; however, 

 this is completely untrue. It is wrong because the basic factor is the 

 necessity of infection of very mobile hosts by the free-swimming larvae 

 of the parasite. In connection with this, the presence of contact between 

 both, in time as well as space, is indispensable. The probability of such 

 a contact under the conditions of extended periods of egg -laying is sharply 

 lowered, inasmuch as among a considerable number, if not the great 

 majority of the forms, the eggs do not remain on the fish. In such a 

 fashion the necessity, which was pointed out by us, arises for an increase 

 in the probability of contact in time and space between the two links of 

 parasitic cohabitation during the presence of favorable conditions of the 

 surrounding medium for the development of eggs and the infection of the 

 host. As we see, this is attained by the decrease of the periods of egg- 

 laying and the concentration of the latter in a more limited region. We 

 note also that the attachment of eggs on the body of the host serves the 

 same purpose--the concentration at the same time of a larger number of 

 larvae within a specific territory. The concentration of the larvae which 

 infects the host is acquired not only by the contraction of the period of 

 egg -laying but also by the rationing of the latter. In separate cases, this 

 apportioning of the egg-laying is carried out differently. 



Thus we saw that anaong a number of worms this is linked with the simul- 

 taneous deposition of eggs joined by filaments, or little feet and filaments, 

 to each other (a number of Microcotyle and others, see page 90), or with 

 the speed of deposition at a determined time of the day or determined con- 

 ditions of the external medium (many lowest forms --Dacty logy ridae and 

 others). Finally, among P. integerrimum t he apportioning of the de- 

 position of eggs is connected with the peculiarities of life activity of the 

 host, because the eggs are ejected in large numbers periodically during 

 the emptying of the urinary bladder of the frogs. 



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