25G ANIMAL PA11ASITES. 



comparison, present the greatest resemblance to the terminations 

 of Burnett's fungus (PI. V, fig. 2, of the Vegetable Parasites, vol. ii), 

 or those of the Hanoverian Leptomitus (PL I, fig. 8, vol. ii), to the 

 level of the hindmost four or five convolutions of the tubular uterus. 

 They appear to replace the vesica seminalis interna or anterior, 

 which is deficient here, and which in form usually resembles the 

 other segments of the testes. The lobate form of the latter is to 

 a certain extent to be recognised in our Distoma, even in the 

 form described. 



In their position, therefore, these structures agree with a great 

 number of the testicles of Distoma, that is to say, they lie in the 

 abdomen behind the ventral sucker, but they occupy an enormous 

 space in the abdomen, in fact the entire space which is left free 

 by the yelk-sacs. The further anatomical structure of these 

 organs is as follows : The above-mentioned convolutions collect 

 into two principal stems, which in general are scarcely thicker 

 than the lateral convolutions. One of these stems lies more 

 in the posterior, the other more in the anterior half of the 

 body. The former ceases therefore in the posterior half of 

 the body, but the latter a little way behind the point of union 

 of the yelk-sacs. This is effected without any particularly 

 marked boundary, without the formation of a clubbed end, 

 or anything of that sort. Quite in front, two more stems 

 are given off right and left, which run on the sides of the animal 

 nearly to the middle of the uterus, are extended and spread out 

 at their extremities, and thus resemble the form of the above- 

 mentioned vegetable parasites. This termination is very well 

 shown by Mehlis in his plate viii, especially on the side which 

 lies to the left of the spectator. The separate stems of the two 

 testicles can hardly be isolated, as each testicle sends out its 

 branches towards the side of the other. We must regard as the 

 anterior ends of the testicles, the points from which a thin 

 filament or efferent duct, ductus spermaticus, springs and runs 

 forwards. These filaments are very thin, of the same colour as 

 the mass of the testicles, and run round the sides of the structure 

 which we called the germ-stock in the female genitalia, at first 

 in a parallel direction, but unite subsequently at an acute angle ; 

 they run directly through their whole course, make no lateral 

 digressions, and pass forwards at the dorsal surface of the animal, 

 concealing themselves behind the convolutions of the uterus, 

 and sometimes making their appearance when the animal is 



