24 t Edmund B. Wilson 



TYPE III 



(NEZARA) 



Egg + spermatozoon = n (male or female, including in each case two equal idiochromosomes). 



These relations are graphically shown in the following diagram 

 (Fig. 6) in which the differential chromosomes are black and the 

 ordinary ones unshaded (only two pairs of the latter shown). For 

 the sake of simplicity only the final result of synapsis (second 

 column) and the ensuing process of reduction (third column) are 

 shown, without regard to variations of detail. The matured eggs 

 (ov) are represented with a single polar body (the result of the 

 reduction-division) which is greatly exaggerated in size. The 

 female-producing and male-producing spermatozoa (sp} are 

 lettered a and b respectively. It will be evident from an inspection 

 of this diagram that the second type may readily be derived from 

 the third, and the first from the second by the reduction (second 

 type) and final disappearance (first type) of one of the differential 

 chromosomes. This I believe to represent the actual relations 

 of the three types. 



II. GENERAL. 



In recent years evidence has steadily accumulated to strengthen 

 the view that the general basis of sex-production is given by a 

 predetermination existing at least as early as the fertilized egg, 

 but there is a wide divergence of opinion in regard to the condi- 

 tions preexisting in the gametes prior to their union. 1 



The fact that in some organisms (such as Dinophilus, Hyda- 

 tina or Phylloxera) the unfertilized eggs, sometimes even in the 

 ovary, are visibly distinguishable as male-producing and female- 

 producing forms, has led a number of recent writers to deny that 

 the spermatozoon can play any part in sex-determination. Beard, 

 for example, asserts that "The male gamete, the spermatozoon, 

 has and can have absolutely no influence in determining the sex 



'The general question of sex-determination, with its literature, has within the past five years 

 been so ably and thoroughly reviewed by Cue'not, Strasburger, Beard, von Lenhosse'k, O. Schultze 

 and others, that I shall here limit myself in the main to an analysis of the new observations brought 

 forward. 



