138 THE INFLIIENCB OF INAKIMATB SUEEODNDINGS. 



forming any decisive conclusion. For instance, far too much 

 value has been attributed in this way to the in-operculated Terres- 

 trial MoUusca {Pulmonifera) ; for, in my opinion, it is "absolutely 

 impossible to form any opinion as to the aflSnities of extinct 

 animals by comparing their shells, which are all that remains of 

 them, sines recent investigations as to living Pulmonifera show 

 that very often species of the same genera have quite dissimilar 

 shells, while, on the other hand, the shells of many species belong- 

 ing to quite distinct genera, or even to different families, are so 

 much alike, that until quite recently they have been considered 

 as species of the same genera. I shall enter more minutely into 

 this subject somewhat later oh. 



Even if we were prepared or obliged to admit that the fossil 

 remains in every instance allowed us to determine the affinities 

 of the species to living animals with absolute certainty — and 

 not in the case of Vertebrata only, but in the Invertebrata also 

 • — still we might assert, and defend the position with success, 

 that the extinct species need by no means necessarily have 

 lived under the same climatic conditions as those forms which 

 are now regarded as their nearest living allies. For we have 

 seen that animals which in separate spots are stenothermal 

 (enduring but a small range of temperature) are able to exist in 

 very dissimilar temperatures when the whole extent of their 

 distribution is taken into consideration; thus Eiiplectella and 

 Semper ella live in a constant warmth of about 15° in the 

 Philippine seas, while their nearest congeners can thrive in other 

 localities in so low a temperature as 1° above zero, which is the 

 temperature of great depths in the Atlantic^ We have seen, 

 moreover, that animals, as parrots, which live almost exclu- 

 sively in the tropics under a mean annual temperature of 26° 

 to 28° with a variation of from 6° to 8° at most, can never- 

 theless subsist in the open air in England, multiply, and even 

 produce new 'sports* or varieties, although living in a mean 

 annual temperature of only 12° to 13°, with a variation between 

 the extremes of as much as 17°- Thus the occurrence of a 

 parrot or of Siliceous Sponges and Crinoids in any geological 

 stratum in high latitudes is not a convincing proof that a 

 tropical climate prevailed during the deposition of that formation. 



