io6 



GENERAL PRINCIPLES OF ZOOLOGY. 



the blood-cells, are distinguished as red and white blood- 



corpuscles. The latter, the 

 leucocytes, are present in small- 

 er numbers and have great 

 similarity to the amoebae found 

 in water; they are lumps of 

 protoplasm, contain a nucleus, 

 devour foreign bodies, as, for 

 example, carmine granules in- 

 jected into the blood, and move 

 in the "amoeboid' manner, 

 i.e., by putting out pseuopodia 

 (Fig. 43). 



FIG. 43 -White blood -corpuscles, a, of 



The red blood-corpuscles of 



vertebrates (Fig. 44), in the mature condition, are circular 

 or oval disks, which by objective influences, e.g., by 

 pressure, may momentarily be bent, incised, or otherwise 



d 



n 



FIG. 44. Red blood-corpuscles. <j, of man; 6, of the camel; c, of the adder; d\ of Proteus 

 (seen from the edge); </", surface view; <?, of a ray; _/", of Petrainyzan; n, nucleus (all 

 the blood-corpuscles are magnified 700 times, except </, which is magnified 350 times). 



modified in form, but cannot actively change their shape, 

 because they no longer consist of protoplasm. Embryo- 

 logically they arise from true, nucleated, protoplasmic 

 cells; whether these cells are identical with the leucocytes 

 is still undetermined ; but later the protoplasmic cell- 

 body changes completely into a plasmic product, the 

 stroma of the blood-corpuscle. If in this metamorphosis 

 the nucleus is retained, there is formed in the centre of 



