196 THE ROYAL SOCIETY OF CANADA 



Fig. 15 of a specimen of C. cornutum from AmhlopUtes rupestris, 

 the same in length as the C. laureatum, shown in Fig. 14, is given for 

 the purpose of comparison. 



A number of small cysts, the largest being 0-23mm. in diameter, 

 containing very young trematodes belonging to the genus Crepido- 

 stomum were dissected out of may-fly nymphs of the genus Hexagenia, 

 sp. ?, taken from the stomach of a Small-mouthed Black Bass from 

 the Musquash River above Flat-Rock Falls and from specimens free 

 in shallow water at Go-Home. The largest of those freed from the 

 cysts measured 0-412 X 0-190, while that shown in Fig. 16 was 

 0-232 X 0-136. The former bore such a close resemblance, when 

 stained and cleared, to individuals of C. laureatum of the same size 

 from the above lots that I consider that in all probability these im- 

 mature encysted forms are the young stages of the latter species, and 

 consequently that the nymph of Hexagenia, sp. ?, is the intermediate 

 host. While, as regards the reproductive organs, only the anlagen of 

 the testes and the structures in the imrnediate neighborhood of the 

 ovary were to be made out, the anterior papillae, suckers and what 

 was considered to be the first appearances of the excretory vesicle, 

 were clearly shown. The latter in all of the preserved specimens was 

 in the form of a large clear space situated posteriorly above the testes, — 

 these being actually flattened against the ventral body wall — and 

 occupying almost the whole posterior half of the worm (Fig. 16). In 

 fresh material this structure was seen to be opaque white and ap- 

 parently solid, like that shown in Osborn's Fig. 2. (20, p. 65) and 

 supposed by him to be "a supply of food for the developing worm," 

 but the applicaton of acetic acid of 50% strength, followed by 70% 

 alcohol, cleared it, by apparently dissolving the contents, and thus 

 rendered the whole worm of a uniform transparency. Sections show 

 that it is a sack with thin walls, in which are numerous nuclei, having 

 as yet no connection, in a specimen 0-36 X 0-13, with a short in- 

 vagination of the cuticle at the posterior end where the excretory 

 pore is situated later. 



No records are at hand of Hexagenia nymphs having been found 

 in the food-contents from the stomachs of the above hosts. 

 23. Centrovarium lohotes (MacCallum). 26, p. 493. 



Intestine of AmhlopUtes rupestris. 



The largest specimen at hand measures as follows: Length, 

 2-35; maximum breadth, just behind the acetabulum, 0-71; diameter 

 of oral sucker, 0-154, of ventral sucker, 0-187; pharynx, 0-102 X 

 0-051. 



