112 NATURAL HISTORY 



This is shewn, magnified, at figure 121. The mouth is 

 situated near the cross, and is capable of assuming a 

 convex form, like the Cercaria orbis. Found among 

 duck- weed in summer. 



196. Cercaria crumena. The bag-shaped Cercaria. — 

 This is a highly-organized animalcule, and probably be- 

 longs to the class Rotatoria, but no wheels have been 

 observed : it has a true alimentary canal, not polygastric. 

 Its form is shewn at figure 123, where the heart-shaped 

 body indicates the bulb, or commencement of the oeso- 

 phagus. It is capable of contracting the head into a 

 conical form. The tail is divided at its extremity. 



197. Cercaria catellus. The puppy Cercaria. — This 

 species I have not examined. Muller found it in stag- 

 nant water in marshes. The head is united to the body 

 by an annular contraction ; it has a double setaceous 

 tail, and the body is capable of being contracted. It is 

 about half the size of the last species. 



198. Cercaria catelina {Diglena catel. E.) — This 

 creature, like the preceding two, belongs to the Rota- 

 toria : its generic characters are given in Book III. It 

 is about l-240th of an inch in length : it has two eyes ; 

 whence its name Diglena : the tail, which is forked, is 

 short. 



199. Cercaria lupus [Cycloglena lupuSy E.) — This 

 species, a sketch of which is shewn at figure 124, is 

 distinguished by a number of minute dots circularly 

 disposed, and called, by Ehrenberg, eyes : its muscular 



