FROM SIMPLE CELL TO COMPLEX ANIMAL. 39 



of the addition of the male nucleus to that of the female in 

 fertilization? Has a similar result ever been attained arti- 

 ficially by means of chemical or other stimuli ? 



2. What suggestions have been offered as to the signifi- 

 cance of the process of maturation? Trace the maturation 

 of the sperm cells more fully. 



3. What classification of ova do the textbooks make? 

 What is the basis of the classification? To what extent do 

 eggs of different animals vary in size, shape, envelopes, etc.? 

 Give examples. 



4. Is there any explanation of the fact that there is such 

 a difference in the amount of food substance in the eggs of 

 different animals? 



5. Trace out by reference to a textbook of embryology the 

 principal changes by which the adult digestive tract is derived 

 from -the simple condition found in the gastrula (archente- 

 ron). What is the fate of the blastopore? How does the 

 permanent mouth originate? 



60. Exercises for the Laboratory. 



The teacher should secure demonstrations of some of the 

 smaller ova (as of the snail, fish, sea-urchin) for examina- 

 tion with the microscope. Compare the ovum taken from the 

 ovary of a hen with a new laid egg, noting especially the 

 structure of the latter. Obtain spermatozoa from the testis 

 of a recently killed animal (as mouse, fowl, etc.) and ex- 

 amine with highest powers of the microscope. If possible 

 secure permanent mounts of segmenting eggs of sea-urchins, 

 showing the 2, 4, 8-celled stages. 



