THE BABBIT. 119 



fertilized) go through the process of division, or segment- 

 ation, as described for the sea-urchin. 



In the embryo of the dog it is twenty-five days before it 

 can be told whether it is to be a mammal or not, and it 

 requires a much longer time to show the distinction be- 

 tween the human embryo and that of the dog. The human 

 embryo and the embryo of one of the higher apes are so 

 closely alike that they are indistinguishable for a still 

 longer time than is necessary to distinguish between the 

 embryos of dog and man. 



The study of development is called embryology. 



Egg-laying animals are called oviparous. If the young 

 develop within the body of the parent, receiving nourish- 

 ment from the blood of the parent, the animal is said to be 

 viviparous ; "or, the young may complete its develop- 

 ment while the egg remains in the interior of the body of 

 the parent, but quite free and unconnected with it, as in 

 those vertebrates which are termed ovo-viviparous." 



THE RABBIT. 



EXTERNAL FEATURES. 



1. Note the shape of the body ; the relative size of the 

 fore and hind limbs ; the length of the ears. Compare 

 the soles of the feet with those of the cat. How 

 many toes has each foot, and how do the claws differ 

 from cat's claws ? 



2. Make a series of dots showing the tracks made by a 

 running rabbit, indicating by which foot each track is 



