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: 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 w^ell authenticated 

 cases where both (jueens and males have been 

 produced in queenless nests, although as a rule sex 

 in ants is determined as in bees, i.e., only males 

 arise from unfertifized eggs. It seems not im- 

 probable in these exceptional cases that one of the 



