SCIENCE-GOSSIP. 



77 



the species might become extinct. In this way we 

 obtain the beginnings, as it were, of new species, 

 which may take a vast period of time before 

 they become thoroughly differentiated from each 

 other. The more rapidly and sharply certain 

 peculiarities separate them, especially peculiari- 

 ties of the genital organs, the more rapidly 

 would their complete separation as species be 

 brought about. 



Specialization of Genital Organs. 

 There appears, however, to be no reason what- 

 ever why changes of the genital organs should take 

 place under changing conditions of environment, 

 such as those just suggested, nor why changes in 

 the genital organs should accompany other changes 

 necessary for greater speed, better concealment, or 

 other habit now assumed to be a matter of necessity 

 to the species. It is evident that the safety of 

 insects depends primarily upon colour (protective or 

 warning), speed, nauseous excretions, development 

 of fascicles of hair in place of simple tubercles, 

 waving flagella, osmateria, discharges of acid and 

 gaseous matters and similar factors, rather than on 

 changes, either in structure or function, of the 

 internal organs. All or any of the various changes 

 just enumerated may be effected without the 

 slightest change in the structure of the genital 

 organs, and hence it is possible for new species to 

 be developed with distinct and conspicuous ex- 

 ternal characters, either in the imaginal, or pupal, 

 or larval, or oval stages, or in all or any of these 

 stages, without any very great modification being 

 necessary in the genital organs. These external 

 characters may be most marked and in every 

 respect specific, as we understand the term. Yet 

 the possibility of successful pairing and the pro- 

 duction of fertile ova between the supposed allies 

 may always be present. 



Variation in Genital Organs. 

 That there is usually some well-marked difference 

 presented by the male genital organs of closely 

 allied species is well known. That these same 

 organs, within the limits of a clearly-defined single 

 species, often offer considerable variation, is also 

 well known. That species with very distinct- 

 looking male genitalia, such as those presented by 

 Anthrocera filipendulae and A. ttifolii, will pair and 

 produce hybrid progeny is an ascertained fact. 

 One is uncertain, therefore, how much structural 

 difference is necessary to prevent successful pairing 

 between, and the production of fertile eggs by, 

 two allied species. So little actual experiment in 

 this direction has been performed that one is 

 inclined to reject the statements laid down as 

 veritable axioms, such as one repeatedly finds 

 relating to this point in the works of even our best 

 naturalists. 



Sterility not a Specific Distinction. 

 No one can read Darwin's remarks on 

 " hybridity," in the " Origin of Species," without 

 recognizing that he was not at all clear how far 

 fertility between allied species was general or the 

 reverse. He was, however, evidently quite clear 

 that the ability of two forms to cross and to 

 produce fertile progeny did not render them any 

 the less two quite distinct species. Yet he assumed 

 that between first crosses there was a tendency 

 to sterility, and that in the intercrossing of the 

 hybrids there was a still greater tendency in this 

 direction. In spite of this, cases are cited by him 

 in which hybrid plants were as fertile as the 

 parent species. He also cites the well-known case 

 of Phasianus colchicus and P. torquatus, and the case 

 of the Indian humped ox being perfectly fertile 

 with the common ox, in each instance the hybrids 

 also being fertile. When one considers the diffi- 

 culties of breeding animals artificially, the ill 

 effects of in-breeding, the individual idiosyncrasies 

 of each animal, the thousand and one difficulties 

 that have to be surmounted in order only to attain 

 a fair amount of success when breeding the same 

 species, it appears evident that we require much 

 more detailed information before any very sweep- 

 ing generalizations may be formulated. 



Incipient Species and Partial Sterility. 



Even Wallace lays it down as a law that, when 

 two incipient species are in process of formation, 

 one condition of their differentiation as distinct 

 species necessitates " some amount of infertility 

 when crossed with the parent form or with each 

 other." Now, it appears to me, once the power is 

 granted for certain species to be able to hybridise 

 freely, somewhat illogical to insist on this as a 

 general principle, and, I must confess that, although 

 I can see the advantage to the incipient forms 

 should such a condition arise, yet I do not at all 

 follow the necessity for it. Wallace supports his 

 view by asserting that the danger of a species, 

 placed under new and adverse conditions, so that 

 it cannot adapt itself to them with sufficient 

 rapidity, is much increased if crossing with the 

 parent form is not checked and afterwards com- 

 pletely prevented except as a very occasional 

 occurrence. He looks upon the means of pre- 

 venting intercrossing as being three in number ; 

 (i) infertility ; (2) the presence of " recognition 

 marks " or external distinctions leading to the 

 preferential mating of similar forms ; (3) physical 

 isolation. He believes that the latter is of little 

 importance, because the majority of new species 

 must arise in the midst of the population of 

 existing species. He thinks, further, that mutual 

 infertility would be usually brought about by 

 natural selection wherever the two forms were in 

 contact ; also that the early occurrence of well' 



