ii2 THE HUMAN SPECIES 



In the pig . . o'6 mm. 



i, dog . 0-44 i 



The lymph cells of man (see Figs. 59 and 60) possess no 

 distinctive characters. They correspond on the whole to those 



of all the vertebrates, 

 and indeed to the blood 

 corpuscles of many of 

 the invertebrates. On 

 the other hand, the red 

 blood corpuscles in man, 

 formed by a metamor- 

 phosis of lymph cor- 

 puscles and white blood 

 corpuscles, are charac- 

 teristic both in form and 

 size. All birds, reptiles, 

 amphibians and fishes 

 possess oblong, ellipti- 



FIG. 58. Human spleen. (Ranke, Der Mensch.) ca ] nucleated, red blood 

 a artery, b vein. 



corpuscles ; the camel, 



llama, alpaca and other members of the same group, as well 

 as the lamprey group of fishes, have oblong, elliptical, non- 

 nucleated blood-cells. The rest of the mammals (with the 

 exception of the camel, llama, etc.) have circular, bi-concave red 

 blood corpuscles, a nucleus being present only during the em- 

 bryonic period, and disappearing at a later stage of development 

 (see Fig. 61). The red blood-cells of man may be easily distin- 

 guished, with the aid of the microscope, from those of other 

 mammals. 



For instance, the blood corpuscles 



of the goat measure 0*0041 mm. 



sheep 0-0050 



cat 0-0065 



rabbit ,, 0*0069 < 



- dog 0-0073 



man 0-0077 



a M. Sussdorf in W. Ellenberger, Handbuch der vergl. Histol. u. Physiol. der 

 Hanssaugetiere, 1887-92, p. 491. 



