Gr. H, F. Nuttall 
817 
that adults only begin to perform their sexual functions on the fourth 
to fifth day after ecdysis. He made rough sketches of pairs in copula 
but never pubhshed them. Sikora (viii, 1915, pp. 523-537) observed 
that copulation may occur ten hours after ecdysis in lice kept at 35° C. 
upon man, and personally I have no doubt but that it may take place 
even sooner. Hase (1915, p. 64, cited by Muller) states that copulation 
lasts 40-70 minutes or more. Muller (1915, p. 43, and pi. iii, fig. 8) 
is the first author who has illustrated a pair in copula: he gives their 
relative positions correctly in a coloured figure of a pair killed in copula 
with chloroform. Whilst he states that the fully extruded “penis 
sack” occupies the vagina, the teeth being directed outward and back¬ 
ward, his figure is incorrect as it only depicts the dilator entering the 
vagina. Finally, Hindle, in his unpublished notes made some two 
years before the outbreak of the present war, records that he observed 
copulation to occur whilst the insects were feeding, and that couples at 
times remained in copula for several hours. 
The foregoing paragraph sums up all that has hitherto been published 
regarding the process of copulation. The paper by Muller became 
known to me through the courtesy of Dr A. E. Shipley, this autumn, 
after this investigation had been practically completed. Muller’s 
description is, however, misleading, and, as far as I am aware, nobody 
has hitherto followed the whole process from start to finish or explained 
the anatomy and functions of the copulatory organs with even an 
approximate degree of accuracy. 
The Author’3 Observations. 
As the result of numerous observations made in the course of in¬ 
vestigations on P. humanius, it has been found that the sexes may 
copulate at any time but that they do so mostly a few hours after 
feeding. To observe copulation, the insects require to be kept warm, 
otherwise they are inactive; a temperature of about 30° C. is suitable 
for the purpose. The following account is based on notes made 
immediately after a pair had been observed to enter into copulation, 
and it may be taken as a typical description of the sexual act. The 
observation was made with a Zeiss binocular microscope, magnification 
X 40, the tube of the instrum-ent being placed horizontally so that the 
pair were viewed sideways and in a good fight. 
The male approached the female from behind whilst she was feeding, 
her abdomen being well raised behind. The male, with the claws of his 
