26 Edmund B. Wilson 



of the offspring" ('02, p. 712); and a similar conclusion, though 

 less dogmatically stated, is reached in the general reviews of 

 Lenhossek ('03) and O. Schultze ('03). The opposite view that 

 the spermatozoon alone is concerned in sex-determination (which 

 like the preceding one, is of very ancient origin) has, however, been 

 maintained by some recent writers, for instance, Block (whose 

 work I know only from Cuenot's review) and McClung, as already 

 mentioned. 1 On the other hand, both Cuenot ('99) and Stras- 

 burger ('oo) in their able reviews, have argued that both gametes 

 may be concerned in sex-determination; and the last named 

 author urged the view, afterward recognized as probable by 

 Bateson and developed in detail by Castle ('03), that sex-produc- 

 tion takes place in accordance with the Mendelian principles of 

 inheritance. 



The observations here brought forward, together with those of 

 Stevens on Tenebrio, establish the predestination (in a descriptive 

 sense) of two classes of spermatozoa, equal in number, as male- 

 producing and female-producing forms. Though indistinguish- 

 able to the eye in their mature state, these two classes differ visibly 

 in nuclear constitution at the time of their formation; and since 

 this occurs in the same order of insects as Phylloxera, where the 

 eggs are visibly distinguishable (by their size) as male-producing 

 and female-producing forms, it is evident that a substantial basis 

 now exists for the views expressed by Cuenot and Strasburger, and 

 for the Mendelian interpretation of sex-production worked out 

 by Castle. Whether in the Hemiptera that form the subject of 

 this paper the eggs are, like the spermatozoa, predestined as male- 

 producing and female-producing forms can at present be a matter 

 of inference only. I have not been able to distinguish such classes 

 by their size, and the data show, almost with certainty, that if 

 they exist they do not exhibit any visible nuclear differences 

 like those present in the spermatozoa. But this gives no ground 

 for denying their existence. No visible nuclear dimorphism of 



J "By exclusion then, it would seem that the determination of this difference (the sexual one) is 

 reposed in the male element" (McClung, '02, p. 78). McClung nevertheless maintained the exist- 

 ence of a selective power on the part of the egg such that " the condition of the ovum determines 

 which sort of spermatozoon shall be allowed entrance into the egg substance" (op. cit., p. 76). 



