450 Animal Biology 



The so-called later stages of dev^elopment (Fig. 221) follow the stages 

 described above. The front limb buds appear and develop into typical 

 front legs. The tail gradually is resorbcd and disappears, the materials 

 beins^ taken to the liver and stored. The internal "ills are resorbed and 

 their place taken with rapidly growing lungs. The adult frog is not 

 aquatic but has lungs similar to other land-living (terrestrial) animals. 

 The coiled intestine gradually shortens, which suggests a typical carniv- 

 orous (flesh-eating) animal, which the frog has now become. 



EMBRYOLOGY OF MAN (MAMMAL) 



Sperm which are produced by the male testes (Figs. 223 and 254) are 

 deposited at copulation in the female vagina and swim by means of their 

 whiplike flagellum through the glandular secretions along the wall of the 

 uterus and finally to the paired Fallopian tubes (oviducts) (Fig. 255). 



e?t»S-Head 



Neck 



-TaLI 



Zona pellucida 



Cijtoplasm 

 Nucleus 



Fig. 223. — Reproductive cells. A, Sperm (spermatozoon or male gamete) ; B, 

 ovum (egg or female gamete). The head of the sperm is primarily nuclear mate- 

 rial; a thin layer of cytoplasm surrounds the nucleus and fills the remainder of 

 the cell. The tail is also known as the flagellum by means of which the sperm 

 moves. The zona pellucida of the ovum is an albuminous envelope. (From 

 Francis, Knowlton, and Tuttle: Textbook of Anatomy and Physiology, The C. V. 

 Mosby Co.) 



The production of ova (eggs) by the female ovary is called ovulation. 

 When the Graafian follicle which develops and encloses the developing 

 ovum collapses and the wall of the ovary breaks (Figs. 223 and 255), the 

 ovum is passed from the ovary into the abdominal cavity near the open- 



