226 EVOLUTION, GENETICS, AND EUGENICS 



er producing eggs and the latter spermatozoa. It is known that all 

 eggs of the hermaphrodite generation have six chromosomes, while the 

 sperms have either five or six. Self-fertilization takes place, and half 

 of the fertilized eggs produce males with (eleven chromosomes) and 

 half produce females (with twelve chromosomes) of the free-living gen- 

 eration. The males of the dioecious generation produce two kinds of 

 gametes with respectively five and six chromosomes, and one would 

 expect males and females to be produced from fertilization; but this 

 is not what happens, for only hermaphrodite individuals with twelve 

 chromosomes are produced. It seems certain that only one of the 

 two kinds of spermatozoa (that with six chromosomes) is viable, and 

 that the hermaphrodite generation is chromosomally female. How 

 can a female produce spermatozoa of two kinds, one with six and the 

 other with five chromosomes? This is explained by the fact that in 

 the second maturation division one of the X-chromosomes remains 

 near the equator of the spindle, and does not become included within 

 the daughter-nucleus. Thus one of the daughter-cells is without an 

 X-chromosome and is male-producing when fertilization takes place. 

 Further investigation of the chromosomes of hermaphrodites will 

 doubtless be in agreement with what we already know. 



Gynandromorphs are individuals made up of some female body 

 regions and some male body regions. Thus, an insect may have male 

 secondary sexual characters on one half of the body and female char- 

 acters on the other; or the anterior end may be male and the posterior, 

 female. The chromosomal basis for these conditions is not entirely 

 clear, but Morgan and Bridges have shown that all of the peculiarities 

 of the hereditary behavior can be explained on the assumption that 

 in the first or second cleavage division one of the X-chromosomes lags 

 behind and is excluded from one of the daughter-cells. Thus one 

 daughter-cell gets XX and the other X, which accounts for the fact 

 that all the cell descendants of one cell have the female characters and 

 all those of the other cell, male characters. 



Intersexes and their bearing on sex determination. — Bridges, dur- 

 ing his experiments with Drosophila, encountered in certain strains 

 anomalous individuals that were neither male nor female, but inter- 

 sexes. On cytological examination these were found to have a changed 

 chromosome complex. One type, for example, was found to have 

 three of one kind of autosomes (instead of the usual two) but only two 

 X-chromosomes. The interesexual condition in this case might be 

 explained by the assumption that the autosomes have a male-produc- 



