132 



ANIMAL BIOLOGY 



Fig. 99. 



- Diagram of the circula- 

 tion of a fish. 



The blood passes from the 

 capillaries into the veins,* 

 which are thinner-vailed than 

 the arteries. These veins carry 

 the blood back to the heart. 

 The heart (Fig. 100) consists of 

 two principal parts; a thin- 

 walled auricle which receives 

 blood from the veins, and a 

 thick-walled, muscular portion 

 called the ventricle, which 

 forces the blood out into the 

 arteries. 



100. Adaptations for breath- 

 ing. — Laboratory study. 



1. Raise the gill covers of a 



preserved fish and find 

 the gills. Carefully 

 separate the gills with 

 the forceps. How 

 many gills are present 

 on each side ? 



2. The openings between the 



gills are called gill 

 clefts.. Gently push a 

 thin strip of wood or 

 the forceps through 

 one of the gill clefts 

 as far as you can. 

 a. In what cavity do the 

 forceps or strip of 

 wood appear ? 



1 This is true of all organs of 

 the fish, excepting the gfills. See 

 101. 



