36 THE LIVEK-FLUKE. 



bands : within is a mass of granular cells. When 

 this larva meets with Limncea truncatula, a small 

 amphibious snail, the head-papilla becomes elongated, 

 and by means of it the larva bores its way into the 

 snail. Unless the larva happens to come across 

 a LimncBa within about eight hours after its escape 

 from the egg, it dies. 



3. Development of the sporocyst. Within the snail, usually 

 in its pulmonary chamber, the ectoderm cells of the 

 larva swell, lose their cilia, degenerate, and are 

 thrown off ; the remainder grows rapidly, and in two 

 or three weeks becomes an elongated sac, '024 inch 

 long. This sac, the sporocyst, has an outer struc- 

 tureless cuticle, a thin muscular layer, and an 

 epithelial layer lining the cavity. 



The eye-spots, though losing their form, persist ; 

 and ciliated excretory funnels are present. Such 

 sporocysts sometimes, though rarely, multiply by 

 transverse fission in the early stages of their develop- 

 ment. 



B. The Second Generation consists of Rediae, which are pro- 

 duced asexually within the sporocyst, and are themselves 

 asexual. 



1. From the epithelium of the sporocyst, cells are budded off 



which segment to form solid masses or morulse lying 

 in the cavity of the sporocyst. Each of these be- 

 comes flattened on one side, and then invaginated 

 to form a gastrula : this increases in size, elongates, 

 and develops into a redia. The redias so formed 

 force their way out of the sporocyst and become 

 free : the wound in \he sporocyst heals, and other 

 rediae are formed in the same way within it. 



2. The free rediae wander about in the snail, increasing in 



size and being especially abundant in the liver. The 

 adult redia (fig. 18) is a cylindrical body about -06 

 inch long, with a collar-hke ridge running round it 



