SEX INHERITANCE 139 
sex-linked and two or three autosomal mutants 
that are semi-lethal to different degrees in the 
female but kill fewer males. One of these sex- 
limited semi-lethals gives only male families under 
certain environmental conditions. 
The sex-ratio in the honey bee has no fixed value. 
At one time of the year all of the offspring may be 
daughters (queens and workers), and at another 
time many sons may be produced. If the sperm 
supply of the queen gives out, or if the queen has 
not been fertilized, all of her offspring will be males. 
The sex-ratio varies therefore from 100: 0 to 0: 100. 
The determining factor for sex is two-fold; an 
internal one producing only X-spermatozoa (that 
accounts for the females) and an environmental 
factor, namely, the conditions that determine 
whether an egg is or is not fertilized. If it is not 
fertilized, it produces a male by parthenogenetic 
development. 
Worker bees that are modified females may on 
rare occasions lay eggs that develop parthenogenet- 
ically. Such eggs produce males. While this is the 
rule for most of the domesticated races of bees, 
there has recently been described a race of African 
bees whose workers readily produce offspring of 
both sexes. In ants also there are well authenticated 
cases where both queens and males have been 
produced in queenless nests, although as a rule sex 
in ants is determined as in bees, 7.e., only males 
arise from unfertilized eggs. It seems not im- 
probable in these exceptional cases that one of the 
