No. 524] CHROMOSOMES AND HEREDITY 



485 



strains) and produce only female spores. Male myeelia 

 will not conjugate with myeelia of the same sign, but 

 readily with the female myeelia. In fact, their sexual 

 behavior is the only way of distinguishing the two kinds 



zygospore produces a sporophyto that in turn produces 

 spores; some of which are male, others female. 



In striking contrast to this case is that of Mucor 

 mucedo. Here also male ( — ) or female (-J-) myeelia 

 are found which unite to form the sexual spore. This 

 produces the sporaugiopliore bearing a sporangium 

 whose spores are all of one or of the other sex, i. e.; all 

 the spores from the single sporangium give rise to males; 

 all the spores from another sporangium gave rise to fe- 

 males. Despite the fact that the zygospore is formed by 

 the union of the two myeelia. male and female, the spores 

 are not mixed, but represent only one sex. Blakeslee 

 points out that this is the same condition found in dice- 

 eious flowering plants, such as the Lombardy poplar, 

 when one seed gives rise to a male tree, another seed to 

 a female tree. In these eases the evidence points to the 

 view that there is no separation of sex units, but a sup 

 pression of one sex or the other. In other words that the 

 basis of sex is the hermaphrodite condition and the uni- 

 sexual form is due to the suppression of one of the dual 



that stand for male and female. 



Let us next turn to the experimental evidence in the 

 animal kingdom. Since the experiments of Doncaster 

 and Raynor on the current moth, Abraxas grossulari- 

 ata, bid fair for years to come to occupy the foremost 

 place in speculations concerning sex I shall bring for- 

 ward this evidence first. 



This species has a rare sport known as Abraxas lacti- 

 color. No intermediate forms between the two exist and 

 none arise from crossing. In nature female specimens 

 only of laticolor have ever been found, although males 

 have been produced artificiallv by suitable combinations, 



