82 
LABORATORY EXERCISES 
The fore legs are developed under the operculum. How soon after 
the hind legs do they appear? 
How long a time is required for the frog to pass through the tad¬ 
pole stage? What is its size at the end of this period? What 
changes must occur with relation to digestion, respiration, and 
locomotion before a frog leaves the tadpole stage? 
EXERCISE 80 (Supplementary) 
REPTILES 
If possible, procure a living turtle (or tortoise) and a garter 
snake for observation in the laboratory. (Much needless fear of 
snakes may be overcome if interest in their habits is aroused.) 
I. The Turtle (or tortoise — land forms are tortoises). What 
is the general shape of the body? What is the character of the 
covering? The upper part of the shell is the carapace; the under, 
the plastron. How many rows of plates do you find on the cara¬ 
pace? Note their markings. If an empty shell of a turtle (or 
tortoise) is available, note its structure. Observe that th^ outer 
plates are of a horny nature and that beneath them is a bony layer. 
Look at the inside of the shell. What does its structure suggest 
with regard to its relation to the skeleton? What is the use of the 
turtle’s shell? Note the shape, the position, and the covering of 
the head. Explain the position of the nostrils; of the eyes. Note 
the character of the jaws. What are the nature, position, and 
covering of the legs? Note the character of the toes. Watch the 
turtle walk and swim. How does it carry on these activities? 
Observe the manner in which the animal protects or defends itself. 
Find out what you can of its food habits. What adaptations has 
it for securing food? 
II. The Garter Snake. Observe the general form and color 
of this animal. What peculiar markings has it? What is the 
nature of the body covering? Note the arrangement and shape of 
the scales. How does the shape of the scales vary on different 
parts of the body? Compare the snake with the turtle. What 
