296 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



The body -louse shows some gregariousness, especially during moult- 

 ing, and a preference for returning to the same spot for oviposition. 

 These habits are shown, though in a less marked degree, by F. capitis. 

 Pairing occurs at any time ; the process may last over an hour, but no 

 upper limit was defined. One male of F. humamis fertilized eighteen 

 out of twenty-one females placed with him in succession. A male of 

 F. capitis fertilized ten females in succession. The longest period during 

 which a female of F. hwnanus retained the power to lay fertile eggs 

 in the absence of a male was twenty days. For F. capitis the longest 

 ascertained time was twelve days. For the two species respectively the 

 usual times seem to he sixteen to eighteen and seven to eleven days. 



The greatest number of eggs laid by any one female of F. humanus 

 was 295, a daily average of 6 "4. Five per diem is common. For the 

 other species the figures were 141, with a daily average of four ; the 

 general average being 3 '7. Fecundity increases with feeding, but the 

 -developing power of the eggs laid was not affected by increased feeding. 



The longest life observed for a male of F. humanus was thirty-two 

 days ; for a female, forty-six (with an average of thirty-four). For 

 F. capitis the corresponding figures were thirty, thirty-eight, and twenty- 

 seven. The longest lives of unfed lice were at temperatures between 

 16° and 18° C. Many Hved three to four days, two for five days, one for 

 seven days. Active specimens of F. humanim survived two days at 

 — 2 '3° C. to - 1'1° C, but none recovered after a week's exposure. 



Under humid conditions at 31° C, 3 p.c. of 1300 eggs hatched on 

 the seventh day, 56 p.c. on the eighth, 33 p.c. on the ninth, 8 p.c. on 

 the tenth, and 0*2 p.c. later, or on the eleventh. The <ig^ period of 

 F. humanus may be estimated at twelve days ; a further twelve days is 

 required for the maturity of the female. " Allowing an average of eight 

 €gg3 per day, spread over a fertility period of forty days, we find that, 

 ■during her hfe, a single female may have 4160 offspring." 



Copulatory Apparatus of Louse.* — George H. F. Nuttall gives a 

 detailed acconnt of the copulatory apparatus in both sexes of Fediculus 

 humanus. Where the subject has been previously approached, it has 

 received scant treatment, and both the structure and the working of the 

 apparatus have been misunderstood. The essential parts of the male 

 apparatus are : (1) the basal plate, (2) the dilator (parameres), 

 (3) the vesica penis, including its rib or strut (statumen penis) embedded 

 in its wall, (4) the penis, and (5) the ductus ejaculatorius. The 

 protrusion and retraction are described. The female apparatus includes 

 a vagina, a vaginal flap, and paired gonopods. The process of copulation 

 is carefully described and figured. 



Inheritance of Sex and Pigment in Lice.f — E. Hindle was engaged 

 before the outbreak of war in some experiments with lice. These were 

 interrupted, but a brief account is published of some bearing on the 

 inheritance of sex and melanism. It appears that in Fediculus humanus 



* Parasitology, ix. (1917) pp. 293-324 (2 pis. and 12 figs.). 

 + Parasitology, ix. (1917) pp. 259-65. 



