VERTEBRATES 109 



Posterior to it, on the dorsal side, is the auricle, a membra- 

 nous sac. 



9. Ventral aorta, arising on the anterior surface of the 

 ventricle as a white muscular " cord " (really a tube) which 

 is enlarged close to the heart into a bulb, the arterial bulb. 

 You should follow up this aorta until you see it divide 

 right and left to send its branches outward into the gills, 

 the branches being called gill arteries. 



Questions. 



1. The fish frequently swallows its food alive. Why 

 should the stomach be muscular } Why is it better that 

 the intestine does not leave the stomach at the end opposite 

 the esophagus ? 



2. Of what use can the cceca be 1 What structure of 

 the human intestine do you recall that is at all like them 

 in form or use .' 



3. How many times the length of the body is the length 

 of the alimentary canal ? Does this indicate that the fish 

 is compelled to eat a great deal of poor food or that its 

 food is highly nutritious, so that little need be taken .' 



4. Near which end of the fish's body is the heart .■' Is 

 this the usual or the unusual condition among animals you 

 know about .' What advantages can you think of in this 

 arrangement .' 



5. What advantages are there in having the heart in a 

 chamber separated from the other vital organs ? 



6. Of how many chambers does the heart consist } Why 

 should at least one of them be muscular .' 



7. How many times does the blood pass through the 

 heart in making a complete circuit of the body .' Would 

 you call this a single or a double circulation ? 



8. Does the heart force the blood onward or does it 



