THE PHYSIOLOGICAL EVOLUTION, ETC. 387 



at 97 the body temperature was 35'3°, and of six observa- 

 tions at 1 9 '4 , 36"2°. 



Finally, on members of the kangaroo family, four ob- 

 servations were made, with the following results : — 



Pterogale xanthopits, 35*9° 

 Macropus giganteus, 3 6 "6° 

 Dendrogaltis grayi, 3 7 '0° 

 Halmaturus bennettii, 37' i° 



In the last two of these animals we see that the temper- 

 ature of placental mammals was reached. For the sake 

 of comparison, a table is appended showing the mean 

 rectal temperature of some of the better known of these 

 mammals. 1 



These we see to vary from 37 "0° for man to 40*2° for 

 the sheep. 



We have now arrived at the true placental mammals,, 

 and it remains for us to inquire how far these resemble and 

 differ from cold-blooded animals in the reaction of their 

 temperature and respiratory activity to changes in the 

 temperature of their surroundings. It is generally stated. 

 that warm-blooded animals differ from the cold-blooded in 

 exhibiting an increased respiratory activity at low temper- 

 atures and a diminished one at high temperatures, and also 

 that the nervous system is able to regulate the heat pro- 

 duction and heat loss so efficiently that the body temper- 

 ature is practically uninfluenced by that of its surroundings. 

 We shall see that under certain conditions both of these 

 relations are departed from, and that thereby a connection 

 with the cold-blooded animals is established. 



As is but natural, these questions of respiratory activity 



1 These data are taken from the table given on p. 790 of Schafer's Text- 

 book of Physiology, vol. i. 



26 



