DETERMINATION OF THE SEX OF THE OFFSPRING 



FROM A SINGLE PAIR OF PEDICULUS 



VESTIMENTI. 



KATHARINE FOOT. 



Nuttall (1917) gives a summary of the data as to the propor- 

 tion of the sexes in Pediculus vestimenli. He says "the propor- 

 tion of the sexes as determined by raising experiments has 

 yielded contradictory results," and this he thinks is due to the 

 small number of the broods of the experiments. In his own 

 experiments of mixed pairs he found the sexes nearly equal, 

 though his broods also were small. 



Hindle (1917) discovered a marked inequality in the pro- 

 portion of the sexes of certain pairs, and he. concludes this to be 

 the normal condition, basing this conclusion on the determina- 

 tion of the sex of 25 single pairs. 



It has been proved by the observations of several investigators 

 that a single female may deposit from one hundred to nearly two 

 hundred eggs. It is obvious, therefore, that the sex must be 

 determined for at least one hundred of a generation or the results 

 are inconclusive. Certainly at least 75 per cent, of the eggs 

 deposited must hatch and the sex be determined for these nymphs. 



Hindle secured such a small number of individuals from each 

 of his 25 pairs that Nuttall seems more than justified in ques- 

 tioning his conclusions. The number of individuals in each of 

 the 25 broods studied by Hindle is as follows: 2, 4, '6, 9, 8, 10, 

 ii, 12, 15, 17, 24, 25, 26, 26, 27, 29, 30, 31, 32, 34, 36, 38, 45, 

 48, 64. Fifteen of these 25 broods were all males or all females, 

 e.g., the brood of two were both females, the brood of four were 

 also females, one of the broods of nine were males and the other 

 brood of nine were both males and females. The brood of sixty- 

 four were all females but as they probably do not represent more 

 than 50 per cent, of the offspring from that pair, the evidence, 

 even in this case, is without force. 



385 



