MAMMALIA. 475 



This family, as far as our knowledge extends, existed during the tertiary 

 epoch, under the same generic form as in our days. Several species of the 

 genus Erinaceus, and one of the genus Ceiitetes, have been found in Europe ; 

 none yet in America, where the living types are also absent. 



The genus Erinaceus (hedgehog) has its body covered with spines instead 

 of hairs, showing thus a resemblance to the porcupine. The skin of the 

 back is furnished with powerful muscles, by which, when the head and the 

 feet are brought towards the abdomen, the animal can shut itself up, pre- 

 senting to its enemies spines all around. The tail is very short, and there 

 are five toes to each foot ; there are six incisors in each jaw, the middle 

 ones being the longest ; on each side three false molars, three true molars 

 bristled with points, and a small one studded with tubercles. 



The common hedgehog, E. europceus {pi. 11^, fig. 18), is common in the 

 woods and hedges, and also in houses. It passes the winter in its burrow. 

 Its skin, it is said, was formerly used to dress hemp. 



The genus Centetes (tenrecs) is composed of four species, inhabiting 

 tropical Africa and the Island of Madagascar. Their body is covered with 

 spines, like the hedgehog, but much shorter ; and the animals do not 

 possess the faculty of rolling themselves so completely into a ball. The tail 

 is absent ; the snout is sometimes elongated, always much pointed ; there 

 are four or six incisors, and two great canines in each jaw ; there are one or 

 two false molars, and four true ones, triangular and bristled ; each foot has 

 five distinct toes, armed with crooked spines. They are nocturnal animals, 

 passing three months in the year in a state of lethargy, although inhabiting 

 the torrid zone. We are even told that it is during the greatest heat that 

 they grow torpid. 



The Oriental or Asiatic hedgehog constitutes the genus Gymnura. 



Ordek 6. Cheiroptera. 



This order is composed of the animals commonly known as bats, and 

 easily distinguished from all other mammals by a membranous expansion 

 Avhich extends from the sides of the neck between the fore limbs and toes 

 down to the tip of the tail, and which enables them not only to sustain 

 themselves in the air, but also to move through it in any direction they 

 may desire. They thus possess the power of true flight as in birds, with 

 which indeed they are frequently confounded. The bones of which the 

 anterior extremities are composed are very much elongated, especially 

 those of the fingers, and constitute an umbrella-like framework, over which 

 is spread & thin, naked membrane continued from the membranous expan- 

 sion of the body. The whole locomotive power of these animals seems 

 concentrated upon this organ of flight. It can only move along a solid 

 surface by folding its wings and using the hooked thumbs to lay hold of any 

 irregularity, and thus draw itself forwards. Hence its motions are awkward 

 and shuffling ; and on a polished surface, like that of a table, it is greatly 

 embarrassed. But in the hollows of trees, the crevices of masonry, and the 



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