450 LECTURE XVI. 



We have seen that the notion of ' species' neither is nor 

 can be fixed^ and that practically every author conceives it 

 differently. Any one who has seen the conchological collection 

 in the Paris Jardln des Plantes, must have observed twenty 

 or thirty species ticketed as races or varieties, which in the 

 British Museum are arranged as well characterised indepen- 

 dent species. Each of these scientific institutions defends its 

 own theory on apparently sufiicient grounds. The one points 

 out the transition forms j the other the distinctive marks in 

 these forms. But this is not the only instance in which natu- 

 ralists differ; and in approaching man, I shall here touch 

 upon the ape. By the side of some well characterised species, 

 about which all are agreed, there are others, e. g. the capu- 

 chin, the brown Cebus, the howHng monkey, and even the 

 orang, which by different authors are divided into dozens of 

 species ; so that it may be asserted that the views as regards the 

 specification of monheys disagree quite as much as those concern- 

 ing that of mankind. Here, therefore, the pi-inciple of muta- 

 bility must play an important part, and there must exist a 

 series of forms which stand in the closest relation to each 

 other. All naturahsts admit, that species occupy only a 

 limited sphere of distribution, which may be wider or nar- 

 rower, and within which they arrive at the greatest perfection; 

 but that at the boundaries of these spheres, these species de- 

 generate, that is to say, assume other forms in order to adapt 

 themselves to altered conditions. That this mutability might 

 go much further and transgress the limits usually drawn 

 for species, we have already shown in the races of domestic 

 animals, which are in fact species. 



From the same example we have also learned that when the 

 surrounding media are unchanged, the production of new 

 species can only be effected by intermixture of allied species. 

 At first, the issue of such commixtures will be raceless masses, 

 the characters of which have no particular constancy ; but by 

 degrees fixed characters are evolved from such masses, which 

 produce a constant race, — a typical species. 



It is clear that so long as the surrounding media remain the 

 same, a typically fixed species will experience but little change. 



