CHORDATA. 



277 



to the true vertebrates than the tunicates are? What 

 do they lack of being real vertebrates? Where is Amphi- 

 oxus found? How large it it? What are the habits of 

 the lamprey? How does its mouth differ from that of 

 the true -fishes? 



291. A Typical Vertebrate (the Frog) : Field and Labora- 

 tory Exercise. Either a fish or a frog may be used for this 

 study, though the author prefers the frog if only one 

 vertebrate is dissected. The student should be encour- 

 aged to make out his own outline and questions with 

 respect to the habits, activities, powers, general form, 

 and structure of the animal. The outlines for the cray- 

 fish and grasshopper (pp. 55 and 66) may be taken as 

 suggestive if desired. 



The following topics should be included and should 

 receive such treatment as the time will allow. 



A. Powers and Activities. Place of living; its habits; 

 methods of locomotion on land and in water, and the 

 effectiveness of them; positions at rest on land and in 

 water ; food and method of capture (experiment by giving 

 it living grasshoppers) ; breathing (make a careful study of 

 all the motions accompanying breathing and interpret) ; 

 length of time it can remain under water; its senses : kinds, 

 and evidences for ; position of its eyes and the advantages 

 and disadvantages of this special position in actual life. 



B. General Form and Structure. Symmetry (compare 

 with crayfish) ; differentiation of the anterior end ; regions 

 of the body, size and relation to one another; all special 

 structures (included in) the head; appendages (com- 

 pare with one another and with your own); joints and 

 digits; all special markings, color, and the like. Make 

 drawings of the frog in the rest position, showing form and 



