268 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



the system of the ductus venosus becomes the hepatic portal system 

 (that vessel being abolished as a continuous trunk), and the 

 ductus arteriosus is reduced to a fibrous cord (ductus Botalli). 



CHAPTER XIL MAMMALIA. 

 17. LEPUS CUNICULUS (The Eabbit). 



THE wild Rabbit, which is here described, forms the parent- 

 stock from which the different kinds of tame Rabbit have sprung, 

 and which differ from it in no essential points of structure. It 

 is, as everyone knows, a gregarious, burrowing animal, of a 

 brownish colour, which harmonizes with the surroundings when 

 it is out feeding, and so serves as a means of protection (protec- 

 tive general resemblance). The short tail is white on its under- 

 side, and is very conspicuous when the animal is moving, pro- 

 bably serving as a " danger signal.'' 



MORPHOLOGY AND PHYSIOLOGY. 



1. External Characters. The bilaterally symmetrical body is 

 divided into the same regions as in the pigeon i.e., head, neck, 

 trunk, and tail. The fore- and hind-limbs are adapted for 

 quadrupedal progression. Almost all the external surface is 

 covered by hair, but a bare perineal space is present on each side 

 near the root of the tail. 



The elongated head tapers in front into the snout, at the end 

 of which is the mouth, a transverse slit bounded by soft mobile 

 upper and lower lips, the former of which is cleft. The external 

 nares are two oblique slits near the tip of the snout, converging 

 in front to the cleft of the upper lip. Long stiff hairs, the 

 whiskers or vibrissce, are present on the sides of the snout as well 

 as in the neighbourhood of the eyes, which are large, and pro- 

 tected by upper, loiver, and third eyelids. Each of the two first is 

 fringed by a row of stiff eyelashes, while the last is a bare opaque 



