290 FRESHWATER LIFE INFUSORIA. 



With regard to external appendages, the three sub-groups of 

 Infusoria are differently furnished. The Flagellata have one or two long 

 filaments hke a whip-lash ; the Acinetce have numerous radiating tubular 

 tentacles, which act as suckers ; and the Ciliata have vibratile cilia, 

 employed as organs of prehension and locomotion. In the last gi'oup the 

 cilia may be distributed over the whole body and be all of one kind, or 

 widely scattered over the surface and of different kinds, or hmited to the 

 under side of the body, or placed in a circlet or short spiral round it. 

 In some species the ciha all move in concert when the animal swims. 

 In others only the smaller cilia at certain points appear to assist locomo- 

 tion, while the larger resemble non-motile bristles and only occasionally 

 move by the twitching of the supei-ficial coat. Certain bell-shaped 

 forms, e.g., Vorticella, possess a tubulai- stalk by which they are attached 

 to water-plants during the principal stage of their existence. This stalk 

 contains a contractile thread, which, on the slightest shock, shortens 

 into a spiral and jerks back the bell. 



Of the ciliated kinds some have the power of secreting a soft 

 gelatinous envelope or an open vase-hke case, into which they retract 

 and from which they extend themselves at pleasui-e. The case is mostly 

 fixed by a very short stem, or by its closed end to some aquatic plant ; 

 but occasionally it is canied about by the animal, which has broken 

 away from its support, and swims freely through the water. Many 

 Infusoria, possibly all, undergo, at certain periods, what is called the 

 encysting process ; that is to say, they enshroud themselves for a time 

 in a gelatinous covering, which hardens into a thin membrane, and 

 meanwhile they become quiescent. The process appears to be sub- 

 servient to pi-eservation through the cold season, or to mixltiplication, or 

 to metamorphosis. '' 



To the above brief description of the class I will now subjoin a few 

 notes on such common examples as have occurred to me in the ponds 

 about Nottingham. Stentor may be looked for at ttU seasons in clear 

 water covered with duck-weed. I have taken specimens in Febi'uary 

 during frosty weather. The body is trumpet-shaped when extended, but 

 is drawn up at times into various figures from obtusely conical to ovate 

 or globular. It often fixes itself by the nai-row extremity, which spreads 

 out a little adhesive foot for the purpose. When free, it swims with a 

 moderately quick rolling motion. The surface of the whole body ia 

 covered from end to end with lines of minute cilia ; while a broken spiral 

 of longer ones suiTOunds the head with a ^vl•eath like a figiu-e of six. The 

 break in the wreath indicates the position of the mouth, near which may 

 be noticed a contractile vesicle and its connected channels. I have 

 occasionally seen three or four transparent vacuoles at a time bulging out 

 from the side of the animal, but they did not contract. The nucleus, 

 when I have observed it, has had the form of a horse-shoe. As to 

 colour, my specimens have been either pellucid, or tinted dull blue, 

 green, or even black, by their granular contents. The last were evidently 

 specimens of .S. niger, and were got from a pond in Bestwood Park ; 

 length, ^\ of an inch. It is iutex'esting to notice diatoms, small 

 animalcules, and so forth, in the food-vacuoles. Instances of self-division 



