CHARACTERS OF SPECIES. 275 



extended, permanent; and are therefore presumed to 

 have had their origin when it came from the hands of 

 its Creator." Domestication and other causes will often 

 produce some variation of these characters ; hut, in a 

 state of nature, such variations are seldom, if ever, 

 perpetuated through many generations. Species are 

 very generally considered the only distinct or definite 

 divisions in nature. But, if this were correct, we should 

 not have some naturalists calling that a species, which 

 others contend is a variety. The theory of variation, 

 again, hy which natural assemblages are regulated, clearly 

 proves that groups are more definite than species. 



(337.) It is difficult, if not impossible, to lay down 

 any general rules for the positive discrimination of 

 species ; hut we may suggest to the student a few of 

 those distinctions which are most absolute : these chiefly 

 relate to form, sculpture, and colour. The form of an 

 animal is as much distinctive of the group it belongs 

 to, as of its specific character ; but so infinitely may the 

 same general form be modified, either in the shape or 

 the proportion of the whole, or of its parts, that, 

 perhaps, the form, rigorously speaking, of no two 

 species is the same. Under the general term of form, 

 we comprehend size or bulk, contour, or shape, and the 

 proportion of the parts to each other. In regard to 

 the first of these, the size of all animals will vary ac- 

 cording to the scarcity or abundance, the richness or 

 poorness, of their food : their size will also be affected 

 by their locality ; that is, by the temperature of the 

 particular climate they have lived in. Animals which 

 are found to be most abundant in cold or temperate 

 regions, will, in proportion as they extend their range 

 to others much warmer, become smaller than their 

 brethren who had not quitted the central region as- 

 signed to the species. The convolvulus sphinx of 

 Europe, judging from the perfect insect, seems to be 

 precisely the same in India as in Australia, in form, 

 colour, and markings ; but the latter specimens are nearly 

 one third less than the European examples; thus showing 

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