244 BIOLOGY: GENERAL AND MEDICAL 



eggs, though such a theory has been held and 

 taught. There is, however, no doubt but that 

 some organisms, especially insects, produce eggs, 

 some of which are male and some female in qual- 

 ity, having morphological differences by which 

 they may be recognized. 



F. That the sex of the offspring is determined by 

 the spermatozoa. In its original form this idea 

 had no scientific foundation, for it was supposed 

 that the spermatozoa from one testis gave rise to 

 male, those from the other to female offspring. 



It began, however, to have significance in a 

 quite different sense, as a result of recent scien- 

 tific investigation of the germinal cells and the 

 mechanism of fertilization. Thus investigations 

 of parthenogenesis showed that unfertilized 

 eggs always develop into organisms of one sex, 

 while fertilized eggs might develop into those of 

 either sex. 



Further significance arose from the discovery 

 by Henking that certain insects like Pyrorchis 

 produce two kinds of spermatozoa in equal 

 numbers. Fertilization by spermatozoa of one 

 kind gave rise to organisms of one sex, fertiliza- 

 tion by spermatozoa of the other kind to the 

 opposite sex. These facts were confirmed by 

 Paulinier, and are now known to be true of more 

 than one hundred different kinds of insects. 



G. That the sex of the offspring is an accident of 

 fertilization. This hypothesis is based upon the 

 discovery in 1908, by Clarence E. McClung, 

 that the spermatocytes of certain insects con- 

 tain an accessory or unpaired chromosome, 

 whose passage into the ovum during the process 

 of fertilization determines the sex of the future 

 product of the fertilization. E. B. Wilson quickly 

 realized the importance of this odd chromosome, 

 which has now been located in the spermatozoa 

 of more than a hundred different kinds of in- 

 sects, arachnids, myriapods, etc. 



