146 On the Reproductive Functional [No. 3, 



table units — species — may at once be discriminated from those diverged 

 forms — varieties — to which they have given rise, and with which, 

 from the important structural differences they frequently assume, they 

 might be hopelessly confounded. Such, at least, is the opinion of 

 those naturalists who regard species as the result of distinct creative 

 acts. On the other hand, those naturalists who believe in derivative 

 h}rpotheses, and look upon all existing organisms as the genealogical 

 connections of other and earlier kinds, entertain the directly opposite 

 view, and maintain that no such essential differences as those above 

 stated exist between the results of hybridism and mongrelism ; though 

 they readily admit a difference in degree. This point has been ably 

 and philosophically discussed by Mr. Darwin, who, after a careful and 

 impartial examination of all the evidence he could collate, considers 

 himself justified in concluding, that " first crosses between forms 

 known to be varieties, or sufficiently alike to be considered as varieties, 

 and their mongrel offspring, are very generally, but not, as is so often 



falsely stated, universally fertile consequently that neither 



fertility nor sterility afford any clear distinction between species and 

 varieties ; but that the evidence from this source graduates away, and 

 is doubtful in the same degree, as is the evidence derived from other 

 constitutional and structural differences."* 



Though Mr. Darwin thus clearly anticipates an essential accordance 

 between the result of hybridism and mongrelism, it is to be observed 

 that the extreme paucity of experimental observations on the latter 

 phenomena prevents his illustrating the subject so fully and satisfac- 

 torily as its importance demands. The want of such observations, 

 and the importance of their bearing on that theory of the " origin 

 of species" proposed by Mr. Darwin, has been frequently and strongly 

 insisted on by Professor Huxley. Thus in his " Essay on Man's 

 Place in Nature," p. 106, we find the following remarks : " Our 

 acceptance of the Darwinian hypothesis must be provisional so long 

 as one link in the chain of evidence is wanting, and so long as all the 

 animals and plants certainly produced by selective breeding from a 

 common stock are fertile, and their progeny are fertile one with another, 

 that link will be wanting." Again in his Lectures on our knowledge of 

 the cause of the phenomena of organic nature, Lecture VI. p. 147, after 

 * Darwin's " Origin of Species," 3rd Edition, pp. 271 and 300. 



