116 THE AMERICAN MONTHLY [May, 



the intermediate host. If the embryo encounters one of these snails it 

 presses its sharp head papilla against some part of the snail's body, and 

 then spinning rapidly on its axis bores into the tissues of the snail and 

 finally forces its passage into the interior. 



3. The Sporocyst. Having entered the snail the embryo loses its 

 cilia etc. and grows into an elongated inert sac, called the sporocyst. 



Generation B. Development of Redia. Certain cells in the interior 

 of the sporocyst become converted by division and differentiation into 

 elongated motile bodies with collar near anterior end, and a pair of 

 pedal processes near the posterior end, etc. When the redia attain a 

 length of about -^ of an inch they burst through the wall of the sporocyst 

 and emerge, and the wound heals up. 



2. Free redia. The free redia passes from the part of the snail at 

 which it is liberated to the other parts, especially the liver, eating its 

 way as it goes, and at last grows to the length of about -fa of an inch. 

 The snail seldom survives three weeks after the entrance of the embryo. ' 

 Germinal cells in the interior of the redia then divide as in the sporo- 

 cyst and give rise to embryos, which may either develop into a second 

 generation for redia, or into a form called cercaria, which is devoid of 

 collar and pedal processes, but possesses a stumpy tail attached to a 

 broad oval body. 



Generation C. i. Development of Cercaria. The embryo, if it is 

 to develop into a cercaria, comes to acquire besides a tail a bifurcated ali- 

 mentary canal, etc., the tail increases in length, but no reproductive or- 

 gans appear. At the sides of the body an accumulation of cells appears 

 and gives the body a milky-white appearance when viewed by reflected 

 light. 



2. Free Cercaria. The cercaria escapes from the body of the redia 

 by a special " birth opening" at the base of the collar, and not by per- 

 foration. Then by the help of its suckers and tail it crawls out of its 

 host, the snail, on to the wet grass. It can now swim very actively by 

 lashing its tail, which is now about twice as long as its body, and can 

 crawl by means of its suckers. 



3. The Cyst. The cercaria soon attaches itself to a leaf or some 

 other object and in a few minutes much mucus is poured out from the 

 whole body, together with granules from the cells just spoken of. 

 During this process the tail is rapidly lashed and at last broken off. 

 Then the mucus hardens and forms a cyst, in which the tailless cercaria re- 

 mains inert until liberated by the solution of its cyst by the digestive 

 juices of the alimentary canal of the mammalian host into which it has 

 passed with the grass to which it was attached. 



4. Mature Sexual Fluke. The liberated tailless cercaria crawls by 

 means of its suckers into the bile duct of the mammalian host, where 

 it grows rapidly. The body elongates, the alimentary canal becomes 

 sacculated, reproductive organs are developed, and the creature attains 

 the condition first described. The first eggs are produced about six 

 months after the fluke's entrance into the sheep, and it is usually sup- 

 posed to live only about nine months, and to pass out of the sheep at 

 the beginning of summer, but it may live beyond a year. 



Henry Mills, of Buffalo, N. Y., died February 7, in Chattanooga, 

 Term., of pneumonia. He was a member of the American Society of 

 Microscopists. 



