38 LABORATORY DIRECTIONS IN 



2d. The cloaca, a continuation of the large intestine, as in the male. 

 Try to discover how the eggs escape into the water. 



Make a diagram of the female reproductive system. Indicate the 

 path of the eggs by means of arrows. 



Compare your diagrams of the reproductive systems of the frog with 

 the charts showing similar diagrams for the other vertebrates. Be sure 

 that you understand the function of each organ in the frog and in a 

 mammal. 



B. METHODS OF REPRODUCTION AND THE TYPES 



OF EGGS 



Full notes on this exercise are desired and particular attention must 

 be given to the conclusions or summaries called for under paragraphs 

 3c, 4d, and E. 



3. Types of Eggs of Oviparous Forms. 



3a. Examine the eggs of two fishes (perch and white-fish) and three 

 amphibians (a frog, a toad and a salamander Ambystoma tigrinum) which 

 are deposited in water and fertilized as laid. Describe the covering and 

 the differences in the way in which the eggs are held in a mass. 



36. Examine the egg of a turtle, a crocodilian, a snake and a bird 

 which in each case is fertilized within the body of the mother and sub- 

 sequently laid in places exposed to air. Describe the difference in the 

 texture of the shell of the two types 3a and 36. Read the paragraph on 

 shell structure in the text-book. 1 



3c. Read the account of fertilization given in the text-book and ex- 

 plain the relation between the habits of the animals in 3a and 36 and t lie 

 nature of the egg-covering. 



4. Types of Eggs of Animals Which Give Birth to Young (Ovoviviparous 

 and Viviparous Forms). 



4a. Examine the demonstrations of the developing eggs in position 

 in the body of an ovoviviparous reptile (the garter snake). Describe 

 the position of the eggs in the genital system and their relation to the 

 body of the mother. 



46. On slides prepared for the purpose locate the eggs in the ovary 

 of a viviparous species (the cat, for example). Note the relative size 

 of the eggs. 



4c. Examine the demonstrations of a mammalian embryo (mouse) 

 in position in the uterus and describe the relation of the developing 

 young to the body of the mother. 



4d. Give an explanation of tin- diflVivnrrs in the relative size of the 

 egg in oviparous, ovoviviparous and viviparous forms. 



1 The frequent references to the text-book iu this section apply to "Principles of 

 Animal Biology," by Shull, Lallueand Ruthven, Chapters IX ;m<l X. 



