How Does Sexual Reproduction Take Place in Vertebrates? 



Vertebrate Reproduction' In backboned animals the reproductive or 

 germ cells are borne in special organs called gonads, and they are usually pro- 

 duced in two different individuals. The gonads are generally paired organs 

 located in the hind part of the abdomen. The eggs, or ova, are formed in the 

 ovary diVid are discharged into the general body cavity. They then pass through 

 a long twisted egg-tube, or ow-duct, eventually reaching the exterior. 



The sperms are produced in spermaries, or testes, and are discharged to the 

 exterior by way of special ducts (see illustration, p. 379). In fishes that we 

 commonly use as food we can often find the ovaries with their masses of eggs, 

 or "roe", in the female specimens, and the corresponding spermaries, or 

 "milt", in male specimens. In the other classes of backboned animals (rep- 

 tiles, amphibians, birds, mammals), the essential organs are the same. The 

 distinctive variations are related to the manner in which the eggs and sperms 



Mature plant 



Section of conceptacle 

 with egg organs and sperm organs 



Egg surroxinded by sperms 



REPRODUCTION IN ROCKWEED, OR BLADDER WRACK 



The eggs and sperms of the bladder wrack are discharged into the water. Numerous 

 sperms swarm around a single egg until one sperm unites with it. The result of the 

 union is a fertilized egg, or zygote 



^See No. 6, p. 395. 



377 



