INTRODUCTION. XXI 



In the majority of Mammals there is little to mark the signs of 

 sex, except superior size and strength, and a different colour in a 

 few; but in certain tribes there are other external marks. The 

 Lion, and a few others, have a shaggy mane, and the males of many 

 Ruminants are adorned with fine horns, either altogether absent in 

 the females, or much smaller. In a few, the canine teeth are greatly 

 superior in size in the males, or only found in them. 



The male generative organs differ much in size and shape, and 

 some are provided with the succenturiate glands of large size, whilst 

 others are wholly without them. The males of some animals have 

 a seasonal development, and at such times only have the power to 

 procreate, whilst others are able at all seasons. Most Mammals, 

 perhaps, are monogamous, a few are polygamous. 



The females of most Mammals have certain periods of heat, or 

 ccstruniy coincident with a catamenial discharge, and will in general 

 only receive the males at these times. The uterus is usually single, 

 but double in a few, as in the Rabbit, with two openings into the 

 vagina. In many of the lower animals, and especially in such as 

 are remarkable for their fecundity, the horns of the uterus are more 

 developed in pregnancy than the body, and the fostus lies there ; 

 as we ascend in the scale the body of the uterus becomes 

 larger. 



The urine is contained in the bladder, which is large, and it is 

 evacuated by a distinct opening in the generative organs, except in 

 the Monotremata, the lowest organized Mammals, where there is only 

 one passage for fceces and urine. The excretory canal in the female 

 is quite separate from the vagina. 



Mammals are silent compared with Birds, and their voice is not 

 generally musical or capable of harmony. It is chiefly employed to 

 call one another, or to express anger, fear, or hunger. 



The skin contains numerous glands and follicles, secreting a 

 lubricating fluid, to maintain it in a moist and supple state. 



In many animals there are special glands in various parts of the 

 body. Some of the Carnivora have special anal glands, which usu- 

 ally secrete a fetid fluid. The Elephant has a temporal gland ; and 

 many Ruminants have both large hollow glands below the eyes, 



