TWO DISTOMES. 253 



II. RENIFER ELONGATUS PRATT. 



This worm was first described by Pratt (1903) from a single 

 specimen, mature but not yet fully grown. The object here is 

 simply to supplement that description, by a comparison with a full- 

 grown specimen. The worm from which the following measure- 

 ments were taken was selected as the largest of about 40 or 50 

 specimens at hand. This worm is 5.5 mm. in length, and 1.7 

 mm. wide at the widest part, while that described by Pratt was 

 3 mm. in length, and .68 mm. in width. The thickness of the two 

 worms is .93 mm. and .4 mm., respectively. 



The oral sucker is round and about .35 mm. in diameter; 

 the acetabulum is decidedly elliptical in outline, extending .82 

 mm. transversely and .6 mm. longitudinally. The corresponding 

 measurements given by Pratt are the following : oral sucker ; 

 length, .32 mm., width, .33 mm. ; acetabulum ; length, .4 mm., 

 width, .36 mm. The relative positions of the suckers on the ani- 

 mal are of course the same. The relative sizes of the various parts 

 of the digestive tracts of the two worms correspond to relative 

 sizes of the worms themselves. 



The most marked difference between the two worms are the 

 greatly increased size of the ascending limb of the uterus, and 

 the consequent displacement of the other organs in the larger 

 worm. In the region just back of the testes, the uterus occupies 

 nearly two thirds of the space within the body walls, and the 

 excretory vesicle is pressed flat against the dorsal wall, extending 

 from one lateral margin to the other. In the region of the testes 

 there is but little diminution in the size of the uterus, and the 

 testes are pressed outward toward the lateral body walls, they 

 themselves being apparently somewhat flattened (see Fig. 3). 

 Forward of the acetabulum, the uterus rapidly decreases in size 

 as it approaches the genital pore. 



The eggs were approximately the same size as those in the 

 smaller worm.- The measurements given by Pratt are .035 mm. 

 by .02 mm. The measurements in the larger worm were .034 

 mm. by .021 mm. 



