46 ILLINOIS BIOLOGICAL MONOGRAPHS [46 



to the bursa copulatrix. The densely massed cells of the glands in the vicinity 

 of the ootype lie just above this organ. The testes are situated at the right 

 side just ventral to the ovary. They are small compact glands, and have no 

 ducts at this stage of development. The vitelline ducts from the diffuse 

 vitelline follicles meet the other genital products in the ootype. The genital 

 bursa is very large and muscular, and hes just ventral to the excretory bladder. 

 Symmetrically arranged glands, with glandular nuclei and hyaUne cytoplasm, 

 empty into it from the postero-lateral reaches. They vary in number from 

 seven to ten on each side. 



With the exception of these glands emptying into the bursa, all of the genital 

 organs of this larva lie in the anterior patelliform region. With the exception 

 of the later formation of a uterine duct between the oot}^e and the bursa, all 

 of the organs are in the approximate location where they wUl be in the adult 

 worm. The massing of the organs in the anterior portion of the animal is 

 undoubtedly correlated with the abbreviation of the appendicular portion of 

 the species. 



The literature on larval hemistomes (Diplostomulum) shows that von 

 Nordmann (1832:34-35, PL III, Fig. 1) has described an egg pouch for D. 

 volvens and two symmetrically arranged testes, with ducts, in the region of 

 the acetabulum. Leidy (1904:111) describing D. grande (Diesing), speaks of 

 "ovaries, dusky yellow." Since the ovary in the Holostomata is single, the 

 organs thus described are possibly testes. 



The bursa is the muscular organ par excellence in Cercaria ptychocheilus. 

 Muscle elements protrude into the atriiun, so that a constriction exists between 

 the anterior and posterior portions of the organ. 



The genital systems of the holostome and the hemistome are similar in 

 those features in which they differ from the distomes. They have modified 

 their primitive genital pore so that it has either become rudimentary or has as- 

 sumed a muscular function. The sperm ducts and the uterine duct empty 

 into the pouch at the posterior end of the animal, instead of the atrium an- 

 terior to the acetabulum. The new genital p)ore is posterior to the ootype, 

 and ventral to the excretory pore. 



C. Distomata. The genital organs of the distomes are different in various 

 families. 



1. Xiphidiocercariae. The genital organs in these cercariae are readily 

 defined with reference to the acetabulum. They are mostly situated in the 

 middle of the ventral side of the larva just behind the acetabulum or shghtly 

 posterior to this position. The ootype is posterior and dorsal to the acetabulum. 

 The uterus coils around the right side of the acetabulimi. It ends in a blimt 

 or tapering ceU mass. Laurer's canal is on the left of the median line, just 

 behind the middle of the acetabulum. It is present in all of the species of 

 stylet cercariae examined. Only in two species are the testicular cell masses 

 outlined. In C. crenata (Fig. 59) these glands consist of two large ovate masses. 



