1 82 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



gases ; the red would appear to be derived from the 

 white corpuscles, and some, at any rate, of these last, 

 owe their origin to the colourless amoeboid corpuscles 

 of the lymph ; this lymph, again, is finally depen- 

 dent for the production of fresh corpuscles on the 

 thicker milky fluid which is found in the lymphatics 

 of the intestines (chyle) ; and this chyle is, of course, 

 due to the metamorphosis of the food taken into the 

 digestive tract, and there converted into peptones and 

 other diffusible bodies. 



The white or colourless corpuscles are amoeboid in 

 form, vary a good deal in size, but are constantly 

 smaller in Mammals than in other Vertebrates, and 

 while, on the whole, less numerous than the red cor- 

 puscles, they vary in number according to the state of 

 fasting or repletion. 



In all Vertebrates save Mammals the red blood 

 corpuscles are provided with a nucleus ; in all Mam- 

 mals, except the camel and the llama, the red discs are 

 circular in form, as they are also in the cyclostomatous 

 fishes ; in the remaining Vertebrates the discs are 

 elliptical. These red corpuscles differ very greatly in 

 size ; largest in the urodelous amphibian Amphiuma, 

 where they measure about T ^- millimetre by -~ ; they 

 are smallest in the Chevrotain (Tragulus), where they 

 are only -^ millimetre in diameter. The interesting 

 researches of Gulliver have shown that, within the 

 limits of any given natural group, the corpuscles are 

 largest in the largest, and smallest in the smallest 

 species of the group. The average number of red 

 corpuscles in a cubic centimetre of human blood has 

 been estimated at five millions ; in the goat there have 

 been found in the same quantity of fluid eighteen 

 millions ; in the rabbit, three and a half millions ; 

 in a cock, two to three millions or more ; in 

 bony fishes seven hundred thousand to two millions, 

 and in various Elasmobranchs from one hundred 



