.I'l 



inflated from the mass of spermatozoids which fills it to excess. During all 

 the remaining tinne it is strongly narrowed and its interior lumen almost 

 completely declines. The prostate glands are also more intensely filled 

 during the period of reproduction. 



The fertilization of worms is achieved through cross- or self- 

 fertilization. Cross -fertilization can occur by means of copulation 

 or without it. Among Monogenoidea which have vaginal ducts insemination 

 occurs through them; among forms without vaginal ducts, just as among 

 digenetic trematodes, it takes place through the uterus. However, the 

 possibility that certain types with vaginal ducts can also be inseminated 

 through the uterus is not excluded. Copulation of Monogenoidea is known 

 only among a small number of species because of the difficulty of obser- 

 vation. This process has been studied best of all among _P. integerrimum . 

 Their copulation takes place in the period directly preceding the egg -laying 

 and sometimes during it. Both worms taking part in copulation remain 

 attached to the urinary bladder wall, they embrace with the anterior ends 

 and alternately introduce their copulatory organs into one or the other of the 

 vaginal apertures and during an hour there can be twenty copulations. The 

 role of the male and of the female is alternately borne by both: now one j jj j 



plays the role of the male, and the other of the female, now the reverse. 

 Because among Polystoma the vaginal apertures on each side of the body 

 are in the shape of a sieve plate, the copulatory organ cannot be fully intro- 

 duced into them but only its chitinous hooks. The period of individual acts 

 of copulation is rather significant; it lasts from one -quarter to one -half 

 minute. Zeller (Zeller, 1876) observed the process of copulation of Poly- 

 stoma and so did we. We have conducted special experiments, the method- 

 ology of which is not without interest. In order to observe the behavior of p. 83 

 Polystoma in natural conditions we immobilized the frog and then opened its 

 ventral cavity, placing the operated animal into a little bath of physiological 

 solution. After the opening of the ventral cavity we introduced the physio- 

 logical solution by pipette through the anal opening into the bladder in such 

 quantities that the bladder would be fully distended and as a result com- 

 pletely transparent. The Polystoma contained therein was studied under the 

 binocular microscope and the observations could be conducted up to 48 hours 

 without any noticeable deterioration in the condition of the host and of the 

 parasites. 



Wilde (Wilde, 1937) described copulation among Dactylogyrus 

 macracanthus Wegener. It lasts from fifteen to twenty minutes and takes 

 place after the worm which acts as the male has already laid its eggs. The 

 worms are seldom observed in copula. During copulation a sperma- 

 tophore is introduced into the vagina and the receptaculum seminis is filled with 

 sperm. However, in spite of numerous attempts we never succeeded in 



observing the copulation of different types of Dactylogyrus ; as a result of i. . 



this we are inclined to think that this process takes place not as simply as '" ' 



it is described by Wilde, and probably is of a different nature. 



Wi 



81 



