CLASSIFICA TION. 



the science of Zoology : it is only by the establishment of classes, 

 and orders, and genera, and species, which constitute, so to speak, 

 the colours of the different regiments, that such arrangement is 

 at all to be accomplished ; and to define the limits and the cha- 

 racters of these genera and species, the efforts of the scientific 

 zoologist are principally directed. It must consequently be our 

 first endeavour to explain what these words, species and genera, 

 mean. 



By Species is understood a number of animals so closely re- 

 sembling each other, that they all might be supposed to be the 

 offspring of the same parents, and in turn to give birth to progeny 

 exactly resembling themselves. The domestic mouse, for example, 

 is a species, the exact facsimile both of its ancestors and its off- 

 spring. Species,, however, may be slightly modified by the con- 

 tinued operation of external circumstances, such as climate, abun- 

 dance or deficiency of food, or other similar accidents ; there may, 

 for example, be a white mouse, or a piebald mouse : fliese are 

 called Varieties of the species. 



A Genus is a group embracing a number of species which have 

 a striking general resemblance to each other in certain important 

 particulars, whereby they are distinguishable from all other 

 animals. The domestic mouse (Mns mnscnlns), for instance, is at 

 once recognizable from the squirrel, the beaver, or the hare, from 

 the circumstance that it has a long tail tapering to a point and 

 denuded of hair; but there are many other animals, which, though 

 evidently not real mice, have this feature in common. There is 

 the rat, Mns rattus ; the brown rat, Mns decnmanns ; the field- 

 mouse, Mns sylvaticns ; and the harvest-mouse, Mns mcssorins, 

 all of which are species more or less resembling the mouse, but 

 all distinguishable from each other by minor characters ; these, 

 therefore, constitute a genus. 



An Order is a far more extensive group, including several 

 genera, allied to each other by some important feature in their 

 economy. The rats and the mice, for example, are all remark- 

 able for their chisel-like front teeth ; but there are other animals 

 that have their teeth of the same coustruction, although they have 

 not the same long and tapering tail, e.g., the squirrel, the beaver, 

 the hare, and the porcupine ; these, therefore, form the order 

 Rodentia, or animals distinguished by their chisel-like teeth. 



A Class embraces all the Orders related to each other by some 

 grand and general character possessed by them all in common. 

 Thus, the Rodentia suckle their young ; but so do dogs, so do 



