108 THE INFLUENCE OF INANIMATE SUnKOUNDINGS. 



Ghilodon cucidlulus is seven seconds, in Euplotes Charon forty- 

 eight. We see at once by this that the active life of the animal 

 is not suspended even at so low a temperature as 5°; for although 

 the pulsations succeed each other more slowly than at a higher 

 temperature, they occur regularly, and the contents of the vesicle 

 are discharged with the same regularity. But if the temperature 

 is still further reduced to 3° or 2° above zero centigrade, the pul- 

 sations of the vesicle, as well as all the movements of the various 

 members of the creature — its cilia, bristles, and so forth — cease 

 entirely; a condition of the animal protoplasm supervenes — 

 which must not be mistaken for death, though it frequently 

 precedes it — to which Eossbach has given the appropriate name 

 of ' chill-coma.' If this chill-coma of the Infusoria is not too 

 long continued, the creature may be revived by raising the 

 temperature ; but if it is long continued, or if the temperature 

 is still further lowered, the animal finally dies. 



Our common pond-snail, Lymnma stagnalis, ofiers a very 

 interesting example of the influence of cold on the organic 

 functions. I found by experiment that this animal, when 

 young, first begins to assimilate food, and consequently to grow, 

 when the water is at about 12" centigrade; at the same time a 

 temperature much below that which induces chill-coma in the 

 Infusoria has no injurious efiect on the animal's life, though it 

 entirely prevents its growth. Indeed, observations have been 

 made which seem to prove that the Lymnsea may be quite 

 frozen up without being killed. This moUusc grows at a very 

 moderate rate ; individuals brought up even under favourable 

 circumstances take about three months to develope a shell 

 twenty-four millimetres long, and they do not attain their 

 full size under two years, although the whole life of the in- 

 dividual can scarcely exceed three or four years at the utmost. 

 Assuming that a young Lymnsea were placed in a lake or stream, 

 of which the temperature constantly exceeds the minimum at 

 which the snail can begin to grow, during only two months of 

 the year, while it never perhaps reaches the high optimum, 25°, 

 the mollusc will be unable to attain its due proportions during 

 the first year, or to grow to its full size even during the second, 

 and thus a dwarfed form will inevitably ariae. This dwarfed 



