ANIMALCULES. 599 



The different kinds of animalcules are very 

 numerous ; on which account I shall confine my 

 observations to a few of the most curious genera, 

 namely Vorticella, Vibrio, and Volvox. 



Of these the Vorticella, or wheel animals, are* 

 the most remarkable both in their structure, their 

 habits, and production. In general form they bear 

 a great affinity to the Polypes, having a contractile 

 naked body, furnished with rotatory organs round 

 the mouth; and indeed many microscopical writers 

 have denominated them Cluster-polypes. They are 

 very small, and generally found in clear stagnant 

 waters, during the summer months, attached to the 

 stalks of the lesser water plants, where they feed on 

 animalcules still smaller than themselves. Many of 

 the species are found in groupes, sometimes formed 

 by the mere approximation of several individuals, 

 and at other times by the ramified or aggregate 

 manner in which they grow. Their various mo- 

 tions, like those oi the Polypes, are generally exerted 

 only for the purpose of obtaining prey, the rotatory 

 motion of their tentacula causing an eddy in the 

 water around each individual sufficient to attract 

 into its vortex such animalcules as happen to swim 

 near : these the little creature seizes by suddenly 

 contracting its tentacula and inclosing them in the 

 midst. The stems of several of the species, into 

 which they occasionally withdraw themselves, are 

 somewhat rigid or scaly. The young are carried in 

 oval integuments on the outside of the lower pact of 

 these; and, when ready to come forth, the parents 

 aid their extrusion, where such is necessary, by 



Q q 4 



