FROM SIMPLE CELL TO COMPLEX ANIMAL. 



from what is popularly known as an egg. The latter term 

 is loosely used to describe the fertilized ovum more or less 

 developed, together with its nutritive and protective coats 

 such as occur around the eggs of birds and reptiles. Ova 

 differ very greatly in size. The largest are found among 

 the birds. The " yellow " of these eggs represents the real 

 size of the ovum. Variations in size are due not so much to 

 a difference in the amount of protoplasm as to a varying 

 amount of food or yolk in the cell. The food may be uni- 

 formly distributed throughout the ovum, mingled with the 

 protoplasm, or it may collect at one pole, forcing the active 

 protoplasm to occupy the other pole (Fig. 8, C). The yolk 

 furnishes food to the young individual or embryo in its early 

 development. 



47. The Spermatozoon or male element is ordinarily in 

 striking contrast to the female. It is typically very small, 



FIG. 9. 



D C 



-H- 



FIG. 9. Types of spermatozoa. A, from the round worm (Ascaris) with a cap, 

 somewhat amoeboid; B, from the Crayfish, with numerous projections; C, from Frog; D, 

 from Sea-urchin, h, head; m, middle piece; n, nucleus; t, tail or flagellum. 



Questions on the figure. What are the chief points of similarity and 

 dissimilarity in these spermatozoa? How do they agree with, and how 

 differ from, the ova in Fig. 8? How do they differ from the average cell? 

 What parts of the structure of typical cells are believed to be represented 

 in the sperm cells? 



