202 



EDWIN LINTON, 



lot collected on July 19. One sporocyst when opened liberated 

 40 cercarise. Some of these were immature. An anterior spine 

 was noted for the first time on these cercarise. It is embedded 

 in the tissues of the head and may be seen protruding its sharp 

 tip at the extreme anterior end in certain stages of extension 

 while the cercaria is actively contracting. What were taken to 

 be excretory vessels were seen extending from near the lateral 

 margins of the oral sucker. They appear to unite in front of the 

 oral sucker and again behind the ventral sucker. There was a 

 large and conspicuous excretory space near the posterior end 

 which communicated with the terminal pore by a slender canal. 



Fig. 4. Free-hand sketches of anterior end, life; showing oral spine, minute 

 spines on suiface of body, and anterior excretory vessels, a, dorsal view. Di- 

 ameter of oral sucker 0.04 millimeter, b, Ventral view of another specimen. 

 Diameter of oral sucker 0.06 millimeter; length of oral spine 0.017 millimeter. 

 From Illyanassa obsoleta. 



A cercaria, flattened slightly and fixed over the flame, had the 

 following dimensions in millimeters: Length o. 24, breadth O. 10, 

 oral sucker 0.041, ventral sucker 0.057, length of anterior spine 

 0.020. The posterior end was truncated as if slightly retracted. 



July 23, 50 snails from a small salt water pond were removed 

 from their shells and carefully dissected; about 350 others were 

 broken open and stirred about vigorously. After a careful 

 search 14 sporocysts were found. The pond from which these 

 snails came, while salt, did not have free communication with 

 the sea. 



In 1910 a lot of snails that had been kept in a dish of sea water 

 for several days were opened on different dates with the following 

 results: 



