SEX DETERMINATION 



211 



sex-potency which was the sum of those of the gametes which had 

 originally been crossed. Thus crossing a pauper a + 3 with a eugametos 

 — I, gave an Fi which formed non-dis junctional gametes with a value 

 of + 2; and the process could be repeated so that crossing this Fi with, 

 say, a paupera — i gave an F2 with a value of + i. The parallelism 



Fig. 99. Relative Sexuality in Ectocarpus. — The drawing on the left shows 

 the conjugation, with many male gametes swarming round a female gamete. 

 The tables on the right indicate by numbers from 1 (weak) to 3 (strong) the 

 "strength" of the conjugation between gametes from different plants. The lower 

 table gives a comparison between the males Nos. 35 and 38; it is apparent that 

 38 is strong, while 35 is weak. In the upper table it will be seen that the weak 35 

 can act as a female towards the strong 38 (and also towards 33). 



(After Hartman.) 



between the chromosome behaviour and the potencies of the sex factors 

 here makes it quite clear that we are dealing with a genetic determina- 

 tion of sex, and further that the sex factors act quantitatively and can 

 be added and subtracted. 



Moewus has reported other results with Chlamydomonas and Poly- 

 toma which he interprets by a hypothesis which involves crossing- 

 over in the 2 -strand stage. This is supposed to bring the + and — 

 factors, which are not allelomorphs, into the same chromosome. This 

 interpretation caimot yet be regarded as convincingly proved. 



