REVIEW OF BIOLOGY OF SEX-DETERMINATION 
19 
schmidt has attempted to explain his results upon a quantitative 
basis, assigning values for the determiners for maleness and 
femaleness together with the postulation that the strength of 
these determiners varies in different races. Thus, the crossing 
of a strong male race with weak male races brings about an up- 
set of the normal conditions and establishes a balance of factors 
where neither one sex nor the other predominates, and thus we 
get the expression of two sets of genes in various parts of the 
organism. Bridges’ recent work on inter sex forms in triploid 
races of Drosophila would indicate that where the normal rela- 
tion of sex genes (located in the X-chromosome) to the autoso- 
mal genes is upset, either by a preponderance of one or the other, 
then sex abnormalities of many sorts may be expected. 
8. HERMAPHRODITISM 
One of the most obscure problems of the entire sex question 
is that of hermaphroditism, the production of ova and sperm by 
a single individual. This condition is found normally in many 
groups of invertebrates: coelenterates, ctenophores, flat worms, 
round worms, annelids, molluscs, and some Crustacea. It is, 
however, the exception rather than the rule and must be viewed 
as a modification of the bisexual condition necessitated to insure 
insemination in animals of a less gregarious nature. Sometimes 
hermaphrodites are female in form, and again they resemble 
more closely males of the group to which they belong. In cer- 
tain nematodes, as in Rhahdites aberrans, an occasional male 
is found among thousands of hermaphrodites of female form. 
Miss Kruger has shown that occasionally there is the failure of 
one chromosome to become incorporated in one of the second 
spermatocytes. Spermatozoa resulting from such deficient sper- 
matocytes may be the cause of those occasional zygotes which 
result in males. Boveri and Schleip have shown that in the case 
of Angiostomum, a nematode in which hermaphroditic individuals 
give rise to a sexual generation, male-determining sperm are 
formed through the failure of one-half of the spermatids to in- 
clude the X-chromosome. Since our knowledge of the chromo- 
