NATURE-STUDY LESSONS. 55 



25. {a) Examine the fin forming the tail of the fish. 

 {b) Spread it out and note its appearance. 



The fin forming the tail of the fish is the caudal fin. 



(c) Draw the caudal fin. 



(d) Compare the upper and lower halves of this 



fin. 



(e) Are they symmetrical or not ? 



(/) What is the special function of this fin ? 



26. Examine the fin on the middle line of the lower 

 surface of the body, just in front of the caudal fin. 



The fin behind the opening into the abdomen is the anal fin. 



27. (a) Point out the fins which grow in the middle 



line of the body above and below. 

 {U) In what direction do they extend ? 

 if) Do they occur singly or in pairs. 



28. («) Point out the fins which grow in pairs. 

 (3) How many such pairs are there ? 



29. Name parts of the frog, the hen, and man which 

 are homologous to the pectoral fins. 



Note. — Organs that develop from like parts are said to be homologous ; 

 e.g., nails and claws ; the wing of a bird is homologous to the arm of a man, 

 but not to the wing of an insect ; the third pair of legs of a spider is homo- 

 logous to the first pair of a fly. 



30. The pelvic fins are homologous to what part of 

 the frog ? of the hen ? of man ? 



31. Draw a minnow or other fish and mark the name 

 of each fin. 



32. By watching the fish in water, discover the special 

 use of the different pairs of fins and of the single ones. 



