Definition of a Species 



a distinct race is produced. And, finally, fresh 

 mutations occur, so that a new species is eventu- 

 ally produced. 



What De Vries calls an elementary species 

 the majority of systematists would call a well- 

 marked variety. 



We may take this opportunity of remarking 

 that the definition of a species is one on which 

 naturalists seem unable to agree. 



So vast is the field of biology, that now-a-days 

 biologists are compelled to specialise to some 

 extent. Thus we have botanists, ornithologists, 

 those who devote themselves to the study of 

 mammals, those who confine themselves to 

 reptiles, or insects, or fishes, or crustaceans, or 

 bacteria, etc. 



Now each class of systematists has its own 

 particular criterion of what constitutes a species. 

 Ornithologists do not seem very exacting. Most 

 of them appear to consider a constant difference 

 of colour sufficient for the formation into a species 

 of the birds that display such a variation. Those 

 who study reptiles, on the other hand, do not 

 allow that a mere difference in colour is sufficient 

 to promote its possessor to specific rank. Into 

 these nice questions we cannot enter. For our 

 purpose a species is a group of individuals that 

 differ from all other individuals in displaying 

 certain well-marked and tolerably constant charac- 

 ters, which they transmit to their offspring. 



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