P. A. Buxton 
l :)9 
pass along the intromittent spicules to the copulatory orifice and duct by 
capillarity. The weakness of this explanation is that it is from beginning to 
end a matter of hypothesis; its strength is that it explains the many peculi¬ 
arities of the parts concerned, such peculiarities for instance as the minuteness 
of the spicules of the male, and of the papilla and duct of the female, and the 
presence of the cup-shaped hollow on the outer ring of the hyposternite. 
THE IMMATURE FEMALE. 
The length of the immature female is 230-250 microns, the breadth about 
195, and the ratio of length to breadth about 100 fco 80. It is therefore slightly 
larger than the male and a trifle wider on the average than male or female at 
any stage; as I have already stated there is a good deal of variation in these 
ratios, and I do not think that they have any practical value as a means of 
separating the stages. The line of division between the notothorax and noto- 
gaster is very indistinct or absent, in this and in the other immature stages. 
The dorsal surface (Fig. 19) resembles that of the adult female in nearly every 
respect. The dorsal epimere of the first leg is very weakly chitinized, and can 
only be found with difficulty; it is probably owing to its imperfect condition 
that an epaulette is not developed. The plastron (pi) is represented by a bare 
rectangular area, smooth and unfurrowed but differing from that of the adult 
in being not darker in colour than the surrounding integument and not sha- 
greened or sculptured. The rudimentary stigma of Megnin ( st ) is present. The 
dorsal armature is conspicuous because the individual cones ( co ), scales (sc) 
and spines (sp) are as large as those of the adult female. The scales stand in 
rather definite rows which are interrupted on the dorsum by the bare area 
(ba)\ this differs from the bare area of the adult in that though it is bare of 
scales it is crossed by integumentary ridges. The spines (sp) are in all respects 
similar to those of the adult, and the formula is 3/4; the last spine of the outer 
row is thinner than the others; possibly Munro overlooked it for he says that 
there are twelve spines in the immature female of S. scabiei. The dorsal lateral 
seta (L 2), and the two anal setae (A 1 and 2) are similar to those of the female. 
The copulatory papilla and its duct are absent, an undoubted fact for I 
have examined a considerable number of immature females. This is very 
subversive of the accepted view that in the Sarcoptidae the immature female 
is the stage in which copulation takes place; the most likely explanation is 
that in the genus Sarcoptes it is the adult female alone which copulates. It is 
an exceedingly unfortunate fact that no one has as far as I know observed 
the act in this genus, and for the moment we must leave the matter in doubt. 
It is to be hoped that further light may soon be shed on this problem, which 
is one of the many interesting ones that remain to be solved. 
The ventral surface is like that of the adult except in the following points: 
the genital operculum, tocostome and its setae are absent; the posterior end 
of the sternum is definitely forked, as is also the end of the epimere of the 
second leg. The capitulum and legs are in all respects like those of the adult 
