104 NATURAL HISTORY 



This species is white, and about the size of the last ; the 

 body is elliptical, the tail short and pointed. Found in 

 infusions of hay. 



180. Cercaria lemna. The duck-weed Cercaria. — 

 The body of this animalcule is capable of being con- 

 tracted 5 but its most usual form is shewn in figure 102. 

 Towards the anterior part two small dots may be disco- 

 vered ', these are considered to be the eyes. The exter- 

 nal membrane of the body is corrugated, and the tail 

 divided into rings in a very curious manner, near to 

 which is a short proboscis, which it can stretch out to 

 about half the diameter of its body : it is situated on the 

 inferior side ; hence some persons have supposed it to be 

 within the body. In creeping, I have observed the crea- 

 ture first to attach its mouth to the glass on which it is 

 placed, then contract its body up towards its mouth, 

 like a leech ; it then fixes the hollow part of its proboscis 

 to the glass, in such a manner as to keep it in the ad- 

 vanced position it has attained, until the head can beset 

 at liberty, and extended to perform a similar operation. 

 During the progression the tail is free. I first discovered 

 it in the month of August, among some healthy con- 

 fervae in a spring near Hampstead : it was very lively, 

 swimming and inflecting its tail briskly. The body 

 measured l-50th of an inch in length. They appear to 

 have a true alimentary canal, not polygastric; but as 

 they escaped before I completed my observations, I could 

 not determine whether they belong to the Rotatoria, not 

 having discovered any cilia. 



