HIGH SCHOOL ZOOLOGY. 



185 



plienomenon occurs in several orders of Mammalia, but nowhere 

 is it more easily studied tlian in the Rodents. . During this 

 period the various functional activities are arrested as much 

 as possible ; there is no food taken and little tissue consumed, 

 so that, as r-espii-ation is also very inactive, the body temperature 

 is assimilated to that of the surrounding medium, and thus the 

 "warm-blooded animals become temporarily cold-blooded. 



39. After the E-odents, the greatest number of mammalian 

 species belong to the bats — Chiroptera^our next order. Here we 

 have a very different modification for aerial life than we liave 

 hitherto met with ; instead of a patagium like that of the flying 

 squii-rels, Galeopithecus and the Phalangers, certain of the 

 fingers and the fore-arm are much elongated, and serve to spread a 

 very delicate hairless web, which extends backwai'd to the thighs 

 and frequently also surrounds the tail (Fig. 117). The thumb 



Fig. 117.— Outline and skeleton of Phyllostoma (after D' Alton), 

 oa, humerus ; va, railius'and ulna ; w, caqius ; I, pollex ; II — V, seco!id to fifth fin- 

 gers ; m and f ' = ■', elongated metacarpals and phalanges ; zf, femiu-. 



alone does not take any part in the support of the web, this being 



chiefiy effected by the third, fourth, and fifth fingers. Except 



in the fruit bats, it is the only digit which bears a claw; in these, 



however, the index also is clawed, although, like the other fingers, 



it is entirely enveloped in the web. The web is very sensitive 



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