OF ANIMALCULES. Ill 



Stationary. I have met with it in various infusions among 

 the Ci/clidia and Cercaria viridis, and also in salt-water ; 

 but it is rather scarce. Lengthy 1 -350th of an inch, 



190. Cercaria tripos is a very singularly-formed ani- 

 malcule : its body is flat, and of a triangular shape, with 

 the mouth situated at the base. It is found in infusions, 

 but is scarce. A magnified view of it is shewn at figure 

 118. 



191. Cercaria tenax. — This is a very minute animal- 

 cule, not much larger than the Monas atomus; very 

 diaphanous ; of an oval form, with the posterior part 

 slightly elongated, forming a short, pointed tail. It 

 whirls about with great velocity. 



192. Cercaria cydidium. The round Cercaria, — This 

 is larger than the last ; slightly oval, w^ith the margin 

 rather darker than the centre : its tail is very short, and 

 is only observed in certain positions of the creature. It 

 is found in clear river- water. 



193. Cercaria orbis. The orbicular Cercaria. — This is 

 shewn at figure 120. It is circular, with the tail formed 

 of two long setaceous hairs on one side, and on the op- 

 posite is situated the mouth. It is found in summer 

 among lemna, and is an interesting microscopic object. 



194. Cercaria discus. The plate-shaped Cercaria, 

 — This is a very small animalcule, rather less than the 

 round Cercaria, with a short, curved tail. Found in 

 stagnant water. 



195. Cercaria luna. The moon-shaped Cercaria, — 



