NATURAL HISTORY OF BHOMPSTON POND. 205 



contractile vacuole (b), and a single large nucleus (c). It is 

 usually less frequently met with than Opalina. 



Among the largest and most beautiful of all the Infusoria is 

 Stentor (fig. 10), a conical or trumpet-shaped ciliated form 

 about l-25th in. in length. It has a peristomial space (a), 

 surrounded by a marginal ring of longer cilia (b), a row also 

 extending to the mouth (c) . Stentor is usually found attached 

 by its narrow aboral end (d) to some algae, and assuming 

 various forms, sometimes becoming ovate or nearly spherical. 

 A comparatively few specimens were met with in this pond. 



On the contrary Oxytricha (fig. 11 side view) is very 

 abundant in the pond. It is a form without cilia on the 

 dorsal convex surface (a), but with a flat or slightly concave 

 ventral surface, bearing cilia and non-vibratile setaa (b) 

 (Hypotricha), the chief organs of locomotion. There are no 

 uncini or styles. It is usually found crawling and climbing 

 by means of the ventral cilia and bristles over the remains of 

 aquatic plants (c). 



Somewhat similar in general appearance is Stylonichia 

 (fig. 12), an animal found hunting amongst the decaying 

 matter in the most stagnant parts of the pond. It differs 

 from the last form in possessing both hooks (a) and styles (b), 

 which are movable but not vibratile. The body is soft, 

 flattened, oval, and flexible, with a ventral mouth fringed 

 with long cilia (c), which cause the occasional darting move- 

 ment. When swimming freely it usually presents its ventral 

 surface uppermost. The rapid and powerful movements of 

 these interesting creatures are most spasmodic, now going 

 forwards, now turning to one side, or rapidly twisting round 

 in a circle for no apparent cause. 



Even more plentiful is Euplotes (fig. 13), a smaller type 

 about 1 -200th in. in length, the distinctive feature of which is 

 the inflexible cuticular protective plate or carapace (a), which 

 is spread over the dorsal aspect of the body only. The ventral 

 oral groove (b) is fringed with long cilia (c), which extend in 

 front ; the hypotrichous processes (d) consist of uncini 

 anteriorly and styles posteriorly. The extraordinary rapidity 



