136 



GENERAL ZOOLOGY 



erythrocytes, white corpuscles or leucocytes, and spindle cells (Fig. 

 86). The red corpuscle is an elliptical disk measuring about 

 22.3 by 15.7m, with a rounded edge and a bulged center in which 

 a single nucleus is located. The red color of the blood is due to 

 the presence of a chromoprotein known as hemoglobin, con- 

 tained in the cytoplasm of the erythrocyte. However, if a thin 

 film of freshly drawn blood is examined under the microscope, 

 the hemoglobin appears yellow rather than red. 



Leucocytes lack hemoglobin and are variable in form and size. 

 Under the microscope, the outline of the leucocyte slowly changes 

 in the manner of an amoeba. The cytoplasm of the living cells 



i 



fr 



* 



scles o 

 C, spindle cells. (After Jordan.) 



c 



Fig. 86. — Blood corpuscles of Rana pipiens. A, erythrocytes; B, leucocytes; 



is colorless, and staining brings out the presence of granules of 

 various kinds. 



The nucleus may be single and rounded or irregular in outline. 

 In some cells the irregularity seems to lead to subdivision into 

 several nuclei (larger cell of Fig. 86, B). The amoeboid move- 

 ments of the leucocytes endow them with independent loco- 

 motion, which enables them to pass through capillaries, into 

 surrounding tissues, without apparently rupturing the walls. 

 They may actually leave the tissues and pass into the alimentary 

 tract. Red cells may also leave through the capillary walls, 

 though less frequently than leucocytes. 



The spindle cells, the third type of blood corpuscle found in the 

 frog, are colorless spindle-shaped cells about half the size of 

 the erythrocytes. They are said to develop from small leuco- 

 cytes and in the spring transform into erythrocytes. However, 

 they may be found as a normal constituent of frog's blood at all 

 times of the year. The fact that spindle cells collect in masses in 



