SECT. ii. INFUSORIA. 79 



Infusoria, remain unchanged for a time within their cysts, 

 being then in a state analogous to the hjbernal sleep of 

 some of the reptiles. The cyst shelters them from cold 

 and draught, and, when heat and moisture are restored, 

 they resume their active vitality. The motions of the 

 Infusoria are probably automatic, and in some instances 

 consensual; they have neither true eyespecks, though 

 their whole body seems to be conscious of light and dark- 

 ness ; nor have they ears ; and, with the exception of touch, 

 which the Vorticellse have in a marvellous degree, it may 

 be doubted whether the Infusoria have any organs of 

 sense whatever, though they avoid obstacles and never 

 jostle one another. The vibrations of their cilia are 

 involuntary as in plants, an instance of the many ana- 

 logies which perpetually occur between the lowest tribes 

 of the two great kingdoms of nature. In both there are 

 examples of propagation by bisection, conjugation, bud- 

 ding, and the alternation of generation, which occurs 

 more frequently among Protozoa than among any other 

 class of animals. There is a perfect resemblance be- 

 tween Zoospores and Protozoa ; they both cease to move, 

 the Zoospore when it secretes its cellulose coat and be- 

 comes a winter or resting spore, the Protozoon previous 

 to encysting, a process presumed to be universal among 

 that class of animals, before subdivision or reproduction 

 begins. It is the dried cysts or germs of the Infusoria 

 that float in the atmosphere as winter spores do, and it 

 is believed that, like the fungi, the same germs may 

 develope themselves into several different forms accord- 

 ing to the nature of the liquid into which they may 

 chance to be deposited ; consequently, it is not necessary 

 that the variety of germs should be very great, although 

 the Infusoria themselves are of numerous forms. 4 



The Infusoria, the smallest of beings, apparently so 

 insignificant, and for the most part invisible to the 



4 ' Lectures on Comparative Anatomy/ by Professor Owen. 



