A. Bacot 
•253 
Tables XII and XIV show the distribution in time of egg laying and 
hatching for the of the series which were afforded the opportunity 
of pairing with a second cj. 
Although the evidence obtained with regard to P. capitis is not so 
full as for P. humanus, it is sufficient to show that the habits of pairing, 
egg laying and fertilization are similar in both species. 
Hybridization. 
An attempt was made to hybridize the two insects with a view to 
obtaining evidence bearing upon the debated question of their right 
to specific rank. It was found that when single pairs were confined 
in the same box, the SS of capitis and of humanus, or vice versa 
paired freely. In half the attempts, however, the of P. capitis were 
killed in the act of pairing or died within a day or two, presumably 
as the result of renewed attempts. It was found necessary, if any 
number of eggs was required, to remove the $ P. humanus after the 
pairing had been consummated. No such precaution was needed in 
the case of the reverse pairing, and although some of the SS of P. capitis 
used died early, they succeeded in fertilizing the eggs. 
A noticeable feature of the pairing between P. capitis d and P. 
humanus $ was the disparity of the sexes in the F. 1 generation of some 
of the crosses. The first trial gave 71 d'c? (= 74 %) against 25 ?? 
(= 26 %), three specimens being killed in the nymph stage. There 
was considerable mortahty in the egg state, which possibly accounted 
for the small number of $$, although it affords no satisfactory explanation 
of the disparity of the sexes. No deaths were observed in the larval 
or nymph stage. 
Pairing No. 2 of this cross gave 130 dd (= 86 %) and 22 ?? (= 14 %), 
44 of the dd had matured before the first $? developed. 
Pairing No. 3 gave 51 dd (= 51 %) and 49 (= 49 %). 
Pairing No. 4 gave 76 dd (“ 68 %) and 35 $$ (= 32 %). 
In the F. 2 and F. 3 generations arising from cross pairing No. 1 
the number of dd and appeared normal in all the boxes whether 
they contained single pairs or the eggs resulting from a number of 
individuals laid in a stock box. A considerable number of specimens 
were preserved without selection and an examination of these insects 
shows the following result: 
F. 2 generation, 211 dd (= 54 %) and 181 ?$ (= 46 %). 
F. 3 generation, 93 dd (= 46 %) and 110 (= 54 %) also 80 nymphs. 
17—2 
