DEVELOPMENT-OF THE FERTILIZED EGG 291 



as in birds, snakes, etc., the eggs, after being laid, are still cared 

 for by the parents, and may be incubated by the parents to 

 keep them warm during their development. All animals that 

 thus lay eggs are called oviparous (Lat. ovum = egg -f- parere 

 = to bear) . A few of the higher animals, like the mammals, 

 retain the egg for some time within the body of the mother. 

 The sperms from the male in these animals are carried into 

 the oviduct at copulation by the penis, and the eggs are fertil- 

 ized while they are still within the oviduct. After the egg is 

 fertilized it attaches itself to the part of the oviduct called the 

 uterus, and here undergoes development. The developing 

 embryo, called the foetus, is nourished through the maternal 

 blood vessels, and grows to a considerable size while still re- 

 tained in the uterus and attached to it by a membrane called 

 the placenta. Eventually, when it has become mature, it is 

 detached from the uterus and expelled to the exterior at birth. 

 The young are well developed at birth, and such animals are 

 spoken of as viviparous (Lat. vivus = alive + parere = to bear). 



