495] LARVAL TREMATODES—CORT 49 



4. Cercaria trigonura mihi from rediae in the fresh-water snail 

 Campeloma subsolidum. 



5. Cercaria columbellae Pagenstecher (1862:305-306) from rediae 

 in the marine mollucs Columbella rustica L. 



Of the two of the above cercariae developed in sporocysts only 

 Cercaria micrura agrees in structure with the characters given for the 

 Cotylocercous cercariae. The only reason for not including it in this 

 group is apparently that it is a fresh-water form. Just why it should 

 be excluded from this group for this reason when it agrees with them 

 in structure is not clear. 



Cercaria myzura Pagenstecher, Cercaria columbellae Pagenstecher, 

 and Cercaria trigonura mihi are the three stumpy-tailed forms which 

 develop from rediae. Two are from fresh-water and one is marine. 

 Both of Pagenstecher 's forms are so insufficiently known that but little 

 structural comparison is possible. Cercaria myzura and Cercaria colum- 

 bellae both have the truncated tail like Cotylocercous group. 



Cercaria trigonura is unique among the stumpy-tailed forms in 

 having a large posterior gland opening at the base of the tail and a 

 bicornuate excretory vesicle. It differs from all except Moulinie's (1856 :- 

 83, 163-164) Cercaria limacis in having a blunted tail, which is not mod- 

 ified as a sucker. 



FURCOCERCOUS CERCARIAE 



Sporocysts containing small forked-tailed cercariae with eye-spots, 

 were found in five out of thirty-eight specimens of Lymnaea reflexa from 

 a small pond in the suburbs of Chicago, Illinois. I propose to name this 

 form Cercaria douthitti. 



The livers of the snails infected with Cercaria douthitti were filled 

 with a tangled mass of elongate, cylindrical sporocysts. The walls of 

 the sporocysts were so thin and in such close contact with the liver 

 lobes (Fig. 63, sw), that it was impossible to free individual sporo- 

 cysts and to follow them to any length. They were irregular tubes of 

 varying caliber, had no free, mobile, club-shaped ends sticking out, and 

 were filled with large numbers of embryos in various stages of develop- 

 ment. (Fig. 64). The walls of the sporocysts were made up of a very 

 thin fibrous layer on the inside of which were scattered nuclei (Fig 63). 



None of the cercariae were found outside of the sporocysts in the 

 snail, but when the liver was dissected large numbers worked their way 

 out. Their progress from place to place was quite erratic altho they 

 moved their bodies and tails vigorously. When in locomotion the body 

 and tail were both somewhat contracted and both moved back and forth. 



