134 DR. J. E. GRAY ON THE SPECIES OF LEMUROIDS, [April 21, 



been so confined ; and some of them have been eveii born in confine- 

 ment, and are probably the hybrid offspring of two species, arising from 

 the intermixture of different kinds in the same cages. Under such 

 circumstances, it is very natural that there should be difficulties in 

 separating them, and that there may be intermediate forms. Yet 

 I may state that, when the specimens which have come under my 

 examination have been carefully compared, I have had no difficulty 

 in distinguishing them, and I have not found a single specimen 

 which I have had the slightest reason to believe is a passage from one 

 species to the other. And this is extraordinary when we consider the 

 very imperfect material that is at our command for the determination 

 of the species of this natui-al genus. In fact it appears to me, after 

 my long experience, that whenever there is any doubt about the 

 distinction of species, it always arises rather from the imperfection of 

 the material at our command, and the consequent imperfection of our 

 knowledge, than from any want of permanence in the species them- 

 selves. It is this that makes me doubt the wisdom of the theorists 

 who would explain the order of the creation by the mutability of 

 species, and take advantage of the imperfection of our knowledge as 

 the basis of their theory, instead of placing their faith in practical na- 

 turalists, who have studied species in detail for years, and who are all, 

 as far as I know, ready to declare that species (the history and detail 

 of which are well known) are the most certain and best defined 

 groups in nature, and are distinctly circumscribed, while genera, tribes, 

 families, orders, and even classes are constantly gradually passing into 

 each other, or contain species, or groups of species, of which it is dif- 

 ficult to say to which group they should be assigned. But, unfortu- 

 nately all their works have too much of the spirit of an advocate, 

 and sometimes there is evidence of special pleading, which is mis- 

 placed in a scientific essay. 



My firm opinion, founded on forty years' experience, and after 

 having had through my hands perhaps more specimens of animals 

 of diff'erent classes than most living zoologists, if not more than any 

 other, is that species are permanent ; indeed they appear to me to 

 be the only groups of individuals that seem to be well defined and 

 separated from other groups by a distinct and unvarying character. 

 I fully agree with the observations of Messrs. Bentham and Hookei', 

 the authors of the ' Genera Plantarum,' now being published, " that 

 on the whole the natural grouping of individuals into species, and 

 their limitation as such, is far more easy and satisfactory than of 

 genera and of all the other superior groups." 



It is no doubt true, as Mr. Darwin observed in his lefter on Hete- 

 rogenesis to the editor of the 'Athenaeum' for the 2.Tth of April 1863, 

 that the " origin or derivation of species from gradual change, how- 

 ever produced, does appear to connect large classes of facts " — that is 

 to say, if such a derivation could be proved ; but, unfortunately, 

 during all my experience, and after most careful search (for the 

 origin of species has always been a most interesting subject of my 

 contemplation), I have never found the slightest evidence for the 

 support of such a theory, or the least modification of any species 



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