THE GENERAL SIGXIFICA^X■E OF AMPHIMIXIS 235 



lias not existed in most of their habitatrs for a long time, speaking 

 phj'logenetically. For this reason we must not over-estimate the 

 significance of the complete persistence of the receptaculum even with 

 exclusively parthenogenetic reproduction. It proves, however, that 

 degeneration of a superfluous organ does not necessarily set in even 

 after hundreds of generations, and in this fact there is certainly 

 a corroboration of the view that it is ' chance ' germinal variations 

 which give the impulse to degeneration. These first induce a down- 

 grade variation through germinal selection, and this, if it concerns 

 an organ of no importance to the survival of the species, is not 

 hindered in its progress bj^ personal selection. Whether degeneration of 

 the receptaculum would have occurred in these parthenogenetic species 

 if they had retained even a periodic sexual reproduction, as is actually 

 the case in the generations of the alternately parthenogenetic and 

 sexually reproducing Aphides, we cannot decide, since we know 

 nothing in either case as to the length of time that parthenogenesis 

 has prevailed among them, nor have we any method of computing the 

 number of generations that must elapse before a superfluous organ 

 begins to vacillate. We only know that the parthenogenetic genera- 

 tions of Aphides no longer possess a receptaculum, while other forms 

 with alternating bi-sexual and parthenogenetic modes of reproduction, 

 which are in this respect possibly more modern, e. g. some of the gall- 

 wasps, possess one similar to that of the Ostracods. 



I must refer to one other case of parthenogenesis, since it has 

 been hitherto regarded as a formidable puzzle for the germ-plasm 

 theor}^, and has only recently found its solution, I mean the facultative 

 parthenogenesis of the queen-bee. As the ' male ' eggs of the bee 

 remain unfertilized, and yet undergo two reducing divisions, which 

 must diminish the number of ids in the ovum-nucleus by a half, 

 the number of ids in the germ-plasm of the bee must be steadily/ 

 decreasing, and this state of things has therefore been regarded by 

 some English biologists as convincing evidence of the untenability 

 of the conception of ids and of the whole germ -plasm theory. 

 Apparently, indeed, it is contradictory to the theory, and we must 

 inquire whether the contradiction is merely an apparent one, dis- 

 appearing when the facts are more precisely known. It was 

 mainly on this ground that I instituted the researches carried out 

 by Dr. Petrunkewitsch, the results of which I have already in part 

 communicated in a former lecture. These results confirmed the 

 previous conclusions that the ' male ' eggs of the queen-bee remain 

 unfertilized, that two reducing divisions occur, and that in consequence 

 the ovum-nucleus onlv contains half the normal number of chromo- 



