OF THE PROTOZOA. CILIATA. 373 



Duration of Life. — "What this may be among the Ciliata is little known to 

 us. **The Infusoria have a comparatively long life " was one of the general facts 

 enunciated by Ehrenberg. ITnder favourable conditions certaiu species have 

 been known to live four or five weeks. This applies to them only in one phase 

 of existence, viz. that which we regard as the normal and mature one. But 

 when we take into consideration the encystuig-process as an act of conserva- 

 tion, we are compelled to assign them a duration of life of a very much longer 

 range ; for by its means the Ciliated Protozoa are preserved in a quiescent, 

 torpid, or hybemating state, not only over periods of di'ought when the ponds 

 containing them may be dried up, but also during the entire winter. 



Further, by the medium of fission and gemmation, the existence of the 

 animalcule is prolonged or perpetuated thi'ough all the multiplied series of 

 di\isions and subdivisions and of gemmation, primary, secondary, and multi- 

 fold, until the chain is broken by a sexual act of generation, and the being 

 perishes in the production of its otEspring. 



The resuscitation of Infusoria, after apparent death, forms a chapter in 

 Ehrenberg's great work ; but the facts discussed have little or no beaiing on 

 this group of Ciliata ; and the marvel formerly attaching to the subject is much 

 diminished by our knowledge of the phenomena of encysting, whether for the 

 purpose simply of self-preservation or the carrying out of the process of de- 

 velopment. 



IifFLrENCE OF External Agents. Heat and Cold. — The Ciliata can sup- 

 port very considerable variations of temperature. Even in winter, beneath 

 the ice, various species may be foimd still living. Ehrenberg tells us that 

 Vorticella microstoma will live after being exposed to a temperature of 8° 

 Fahr., and the ice gradually thawed ; in fact, however, not more than one in 

 a hundred will survive this process. Below this temperature none can live. 

 The same is true of Paramecium Aurelia, Cyclidium Glaucoma, Glaucoma 

 scintillans, and Colpoda Cucullus. When death is caused by cold, no rupture 

 or injury of the body is perceptible, except in the case of Cliilodon Cucullulus 

 and some few other species, which are frequently quite disintegrated and dis- 

 persed. Stentor polymorphus and S. Mulleri will not live many hours at a 

 temperature of 9° Fahr. ; and arborescent Vorticella, subjected to the same 

 degree of cold, faU from their stems and die. 



Perty gives a ILst of about 40 species of Ciliata which he found in Switzer- 

 land during the cold of winter, beneath the ice ; we name a few as a guide to 

 investigators : — Coleps hirtus (often without a shell), C. inermJs ; Oxytricha 

 pellioyiella, 0. caudata, 0. prisca, 0. gihha ; Pleuronema crassa ; Eitplotes 

 stnatus ; Vorticella patellina ; Stentor Rosellii ; Paramecium Colpoda, P. 

 versutum, P. leucas; Trachelius Anas, T. Lamella, T. Meleagris ; Trachelocerca 

 Olor ; Glaucoma scintillans ; Lacrymariarugosa ; EncJielys Farcimen ; Cliilo- 

 don Cu^idhdus ; Spirostomum ambiguum ; Amphileptus Fasciola, &c. 



Ehrenberg affirms that when animalcules are fi"ozen in ice, they are as it 

 were lodged in a Httle cavity, and suiTOimded by water. This circumstance 

 he imagined to be due to their animal heat, — an explanation too improbable 

 to be admissible ; and, if the observation be correct, it must give place to some 

 other. 



Respecting the effects of cold, it is a general law of the Ciliata, that their 

 numbers rapidly diminish when winter sets in, and that, on the contrary, 

 they rapidly augment so soon as the warmth of the sun in spring manifests 

 itself, and continue to increase in number and variety until the height of 

 summer is passed. 



Their endm-ance of heat is almost equally extraordinary as that of cold. 

 Some are found in hot springs : thus Perty found specimens in the hot springs 



