DEGENERATE SEXUAL REPRODUCTION. ^7 



(2) He also allows that it does degenerate in the summer aphides, 

 where the periodic disappearance of males is well known. (3) In spite 

 of the absence or else futility of impregnation in rotifers, we find the 

 males obviously in process of degeneration. 



In conclusion, we believe with Weismann and others, that the 

 absence of fertilization is a minus in evolution, but see no warrant for 

 supposing that it absolutely precludes either progress or the reverse. 

 The power of parthenogenetic birth has two different results. (1) 

 The female cell has a certain inaleness about it ; it retains the stimulus 

 which the male element usually affords ; the species will therefore be 

 frequently of active male-like habit, for example, rotifers and water- 

 fleas. (2) On the other hand, the long-continued production of 

 females means an anabolic preponderance, a weighting of the species; 

 and this is seen in the sluggish plant-lice, coccus-insects, and the like. 



VII. Peculiarity of the Parthenogenetic Ova. — -Before a 

 theory of parthenogenesis is sought, the natural question arises, Are 

 these eggs that develop of themselves in any way peculiar ? (a) For 

 a while it was supposed (for example, by Balfour) that parthenogenetic 

 ova did not form polar globules, and the theory based upon that 

 regarded the retention of these bodies as taking the place of fertili- 

 zation. The demonstrated occurrence of one polar globule in several 

 parthenogenetic eggs partially demolished this theory, and it is only 

 within the last two or three years that it has been restated in accurate 

 form, (b) Simon shrewdly points out that in some of the most 

 marked cases of parthenogenesis the sex-cells are insulated from the 

 body at a very early stage. This is notably so in those midges which 

 reproduce parthenogeticaliy even before maturity. It is certainly 

 striking that these forms should unite an extreme earliness in the 

 embryonic separation of the germ-cells with a most precocious 

 reproduction. These germ-cells are ova which have a much less 

 circuitous history than in most cases; they have far fewer cell-divisions 

 behind them, they have thus a reserve power of division which other 

 ova have not; they are able, in fact, to develop of themselves. This, 

 unfortunately, is not known to be true of some of the most signal 

 cases of parthenogenesis (for example, rotifers) ; but it is true of some, 

 and that to a greater extent than was known when Simon wrote. On 

 the other hand, some forms where parthenogenesis is unknown (for 

 example, leeches and Sagitta), also exhibit the same early differentia- 

 tion of germ-cells, so that we can only look upon the fact as one of 

 the auxiliaries of parthenogenesis. 



(c) The peculiarity of parthenogenetic ova, which has of late 

 attracted much attention, is that they extrude only one polar cell, — 

 not two, like other eggs. This discovery is due to Weismann, who, 



