554 INFUSORIAL ANIMALCULES 5VORTTCELLINJE. 



condition. It is often very difficult to distinguish the Monads 

 from the young of other species, which they much resemble. 

 Where a number of minute gelatinous points are seen in the 

 neighbourhood of clusters of larger forms, they are probably to be 

 regarded as their germs in a state of development. 



1217. The Vorticell'mcB are a very interesting family to the 

 microscopic observer, from the variety of their forms and actions, 

 and from their great abundance in most pools in which vegeta- 

 tion is going on. The ciliary action is here very distinct and 

 powerful; and the Animalcules show by their movements a 

 great susceptibility to external impressions. Thus, the common 

 Vorticella (Fig. 728, a\ which clusters round the stalks of duck- 

 weed, is usually attached by a long peduncle, which, when the 

 animal is seeking for its prey by the vibration of its cilia, seems 

 fully extended, and almost put on the stretch. But if the stage 

 of the microscope be smartly tapped, the Animalcule is seen to 

 contract its peduncle suddenly ; and it afterwards slowly extends 

 it when free from alarm. In the Stentor (Trumpet Vorticella), 

 which is one of the largest of the Polygastrica, the body is itself 

 prolonged, and attached at its basis. In the Vaginicola, each 

 animalcule is enclosed in a delicate horny sheath, within which 

 it can retract itself at pleasure ; and the Ophrydium, another 

 allied form, constitutes large gelatinous masses, in which a vast 

 multitude of animalcules are imbedded. The true Vorticellce 

 are able to change their dwelling-place in a singular manner. A 

 fringe of cilia is produced at the lower part of the body, and 

 when this is complete, the animal quits its stalk, and swims 

 away freely in search of a new point to which to fix itself. Some 

 of them produce buds from their sides, like the Hydra ; and 

 others multiply by subdivision. Both these processes take place, 

 if the temperature be genial, and the animals be well supplied 

 with food, with great rapidity. By the older observers, those 

 which were seen during their change, and whose form was thus 

 very different from the one usually observed, as also those that 

 were seen in their unattached condition, were regarded as dis- 

 tinct species. In some genera belonging to this group, we ob- 

 serve the stalks of a number of individuals proceeding from one 



