66 



THE BLOOD. 



FIG. 24. 

 Mammals. Birds. Reptiles. Amphibia. 



Fish. 



The above illustration is somewhat altered from a drawing, by Mr. Gulliver, in the 

 Proceed. Zool. Society, and exhibits the typical characters of the red blood-cells in 

 the main divisions of the Vertebrata. The fractions are those of an inch, and rep- 

 resent the average diameter. In the case of the oval cells, only the long diameter is 

 here given. It is remarkable, that although the size of the red blood-cells varies so 

 much in the different classes of the vertebrate kingdom, that of the white corpuscles 

 remains comparatively uniform, and thus they are, in some animals, much greater, 

 in others much less, than the red corpuscles existing side by side with them. 



It may be here remarked, that the appearance of a nucleus in the red blood-cells 

 of birds, reptiles, amphibia, and fish, has been shown by Mr. Savory to be the result 

 of post-mortem change; no nucleus being visible in the cells as they circulate in the 

 living body, or in those which have just escaped from the bloodvessels. 



