26 Dentition and Characters 



ing object is to make known the existence of three distinct types of 

 dentition existing amongst the shrews, and to direct attention to the 

 characters afforded by the teeth, as much more deserving our confi- 

 dence than some of those usually resorted to for establishing speci- 

 fic differences in this genus. It has been the practice of naturalists, 

 in describing these animals, to dwell too much on the colour of the 

 fur, and on the form, as well as the relative length of the tail. M. 

 Duvernoy has shown that these points afford very uncertain charac- 

 ters ; and my own recent examination of numerous specimens leads 

 me to accord entirely with his opinion. Not only does the colour 

 of the fur vary in its tints with age, sex, and season, but in the 

 mode according to which the tints are distributed. M. Duvernoy 

 observes, that in some individuals of the S. araneus the under parts 

 of the body are pale grey, whilst in others these parts are the darkest. 

 He adds, that the upper parts of the body will vary in the same 

 species from greyish-brown or black to a decided red. My own 

 observation has led me to remark further, that the colours are not 

 even constant in individuals of the same age ; nor is there appa- 

 rently any fixed relation between the period of growth and the na- 

 ture of the prevailing tint. In some instances I have noticed young 

 individuals as dark as, or even darker than, full-grown specimens 

 of the same species ; in others, young which were of a lighter rufous 

 than any adult that I had ever met with. The characters of the 

 tail, at least those derived from its form, seem to depend chiefly 

 upon age. It is generally shorter in proportion, and always thicker, 

 in voung than in old individuals. This last circumstance is due in 

 part to a copious growth of elongated bristly hairs, which closely 

 surround the tail in young specimens, at the same time standing 

 rather out, but which either fall as age advances, or become so worn 

 from friction as finally to leave this part, in very old individuals, 

 nearly naked. It is also manifestly due to a greater plumpness of 

 the tail at this period. In after life, the muscular portions, as well 

 as the investing skin, sometimes shrivel, so as to render the angles 

 of the included vertebrae more apparent ; hence entailing not only 

 a diminished thickness of the tail, but, what is equally obvious in 

 adult specimens, a change in its form from cylindrical to nearly 

 square. With reference to this last point, M. Duvernoy observes, 

 and I believe correctly, that the quadrangular form of this part is 

 common to several species, but that it never appears till after a cer- 

 tain age, the tail in young subjects being always round. There is 

 also a stricture sometimes observable at the base of the tail, which it 

 is of importance to notice, because it was considered by Hermann as 



