47 



striliing examples from animals familiarly known, concludes 

 that — " The cases of persistent fertility in hybrids are certainly 

 not frequent, but they are, nevertheless, so well certified 

 that the contrary statement is in plain contradiction to fact." 



What, then, it may be asked, are we to abandon all idea 

 of species ? Certainly not. To do so would be to abandon 

 all attempts at classification, for in degree, the same objection 

 will apply to all sharply defined demarcations between genera, 

 families, orders, classes, nay kingdoms. The expression that 

 '' no absolute species exists," merely lays stress upon the 

 fact that the type of the group termed sjpecies is fixed upon 

 mainly to define the maximum of relatively constant charac- 

 teristics around which all the individual varieties may cluster, 

 and which shall serve to distinguish the type species from a 

 closely allied group of a similar character. Indeed we may 

 picture species as the nodes of an irregularly moniliform 

 series, whose extremities are in some cases sharp and distinct, 

 and in other cases mere constrictions, where the extreme 

 individuals of each node or group meet, and can hardly be dis- 

 tinguished from each other. But even when we clearly under- 

 stand, and agree with each other as regards the principles 

 which determine classification, it is often perplexing to fix upon 

 characters whereupon to erect the standard of a species or 

 variety, for it is well known in practice that characters are 

 seized upon rather from stability and association with certain 

 other characters than from absolute difference in particular 

 features. Gwyn Jeffreys thus defines the degrees of difference 

 which should determine species : — " They constitute more or 

 less extensive groups of individuals which resemble each 

 other as well as their parents and offspring to the same 

 extent as we observe in the case of our own kind. These 

 groups to deserve the name of species must be distinct from 

 others : because, if any of them are so intimately blended 

 together by intermediate links, so as to make the line 

 of separation too critical, the test fails, and a subordinate 

 group, or what is called a ' variety,' is the result. 

 For this reason it is indispensably necessary to compare 

 as great a number of individuals as possible, and espe- 

 cially a series of different ages and sizes, commencing ah ovo, 

 as well as specimens collected from various localities." And 

 again, he states in respect of what are termed varieties, that 

 " the characters by which they usually differ from species con- 

 sist of size, comparative proportions of different parts, colour, 

 and degree of sculpture ;" and he remarks that such dif- 

 ferences " originate in some peculiarity of climate, situation, 

 composition of soil or water which they inhabit, the nature or 



