284 



REPRODUCTION OF ANIMALS 





t.est.isf 



i?- 



Fish seldom show secondary sex characters. 

 The sex organs are the ovaries in the female, and 

 the testes in the male. The ovary produces nu- 

 merous ova, each of which contains a yolk and a 

 nucleus. The testis produces numerous sperms, 

 each of which has a nucleus, a head, and a 

 motile tail. 



-heocdL , 

 nucleus 



-tccil. 

 cytoplorsm. 



river fish spawn in the ocean. So powerful is the urge to spawn 

 in natural spawning grounds, that the salmons will leap falls or 

 artificial barriers in their eftorts to reach quiet water on their way 

 from the deep sea. Many die of exhaustion on their w^ay if they 

 meet too many obstacles. Those that surmount the barriers usu- 

 ally die soon after spawning. 



Production of eggs. Certain organs of the frog are specialized 

 for the production of gametes. In the female, the two ovaries 

 secrete hundreds of tiny ova. The ovaries may be compared to 

 the ovaries or pistils of flowers which produce egg cells. Ovaries 

 are common to all females in the animal kingdom. The ova of 

 the frog go through a maturation process in which the number of 

 chromosomes is reduced one half. This process results in the 

 production of mature gametes. The mature ova reach the body 

 cavity of the frog and then pass through the tubes called oviducts 

 into the cloaca. They leave the cloaca by means of an open- 

 ing at the posterior end of the female frog's body and pass into 

 the surrounding water. Ova are characterized by their compara- 



