n8 



BEGINNERS' ZOOLOGY 



its lungs. Why? The heart of a fish is near its gills for the same 

 reason. The heart has one auricle and one ventricle. (Coloured 

 figure i.) 



Blood returning to the heart comes through several veins into a 

 sinus, or antechamber, whence it passes down through a valve 



Fig. 221. — Plan of Circulation. 



Ab, arteries to gills; Ba, aortic bulb; V, ventricle. 



into the auricle ; from the auricle it goes forward into the ventricle. 



The ventricle sends it into an artery, not directly, but through a 



bulb {as, Fig. 220), which .serves to maintain 

 a steady flow, without pulse beats, into the 

 large artery {aorta) leading to the gills. The 

 arteries leading from the gills join to form a 

 dorsal aorta (Ao, Fig. 221), which passes 

 backward, inclosed by the lower processes of 

 the spinal column. After going through the 

 capillaries of the various organs, the blood 

 returns to the heart through veins. 



The colour of the blood is given by red 

 corpuscles. These are nucleated, oval, and 

 larger than the blood corpuscles of other ver- 

 tebrates. The blood of the fish is slightly 



Fig. 222. — Brain of above the temperature of the water it in- 



PERCH, from above. habits. 



Notice the general shape of the brain 

 (Fig. 222). Are its subdivisions distinct or 

 indistinct? Are the lobes in pairs? The 

 middle portion of the brain is the widest, 

 and consists of the two optic lobes. From these lobes the optic 

 nerves pass beneath the brain to the eyes (Sn, Fig. 223). In 



«, c-nd of nerve of smell; 

 an, eye; v, s, »i, fore, 

 mid, and hind brain; 

 /;, spinal bulb; r, spi- 

 nal cord. 



