192 



BIOLOGY 



corpuscles (erythrocytes) (Gr. erythros = red + cytos = cell) (Fig. 



93 re), are oval in shape; their red color is due to the haemo- 

 globin, which is in the cor- 

 instead of in the 

 as in the case of 



rc . 



, . 7:L .. I* ~ 



in. mm 



FIG. 93. BLOOD OF THE FROG, HIGHLY 

 MAGNIFIED 



lu, leucocytes or white corpuscles; 

 rc, red corpuscles. 



puscles, 

 plasma, 



the earthworm. The white 

 corpuscles (leucocytes) (Gr. 

 leukos = white + cytos = 

 cell), lu, are smaller than 

 the red corpuscles, and are 

 able to force themselves 

 through the walls of the 

 capillaries, and wander in- 

 definitely through the tis- 

 sues. There is a third type 

 of very minute bodies in the 

 plasma, called platelets, of which little is known. 



Lymph System. Besides the blood vessels, the frog has a 

 system of much smaller lymph vessels in the skin, the intestine, 

 and other parts of the body. These are thin walled and filled 

 with a colorless liquid, the lymph, and are so delicate the,t 

 they can be seen only in specially prepared specimens. In 

 places these vessels are connected with spaces between the 

 tissues, lacunae, and with the large cavities of the body. In 

 the intestine the lymph vessels receive a special name, the 

 lacteals. Lymphatic glands are found in connection with the 

 lymph vessels, and in the frog there are also two pairs of lymph 

 hearts, whose contraction propels the lymph in its circulation. 

 The Nervous System. The nervous system consists of: (1) 

 The cerebrospinal axis, (2) The cranial nerves, (3) The sympa- 

 thetic system. 



Cerebrospinal Axis. The brain and spinal cord are on 

 the dorsal side of the animal, within the neural canal and the 

 cavity of the skull; Fig. 94. The brain consists of several 

 distinct parts. Beginning in front they are as follows: The 



