138 
Sarcoptes 
in Fig. 18); this passage opens in front at the bottom of a cup-shaped depres¬ 
sion on the outer ring, and behind in the concavity of the inner ring. This 
passage contains the intromittent spicules. The third piece of the hyposternite, 
the lateral rod (Ir), lies at the side of, and dorsal to, the outer ring. As I have 
said the intromittent spicules (is) pass through the passage in the inner and 
outer ring of the hyposternite, and their tips can be seen in the cup-shaped 
hollow at its end. They arise from a chitinous body, the “penis” of Robin; 
as I do not believe that this is an intromittent organ, I shall call it the basis 
penis (bp). It is shaped like a castle, with four projections like battlements 
upon its free anterior margin. It is from the two median projections that the 
intromittent spicules arise. At its posterior end the basis penis is wider and 
passes gradually into transverse folds of the integument. 
The manner in which these very complicated genital structures are em¬ 
ployed is not certainly known; so far as I am aware jlo one has ever observed 
Sarcoptes in copulation, and we must presume that the act is performed very 
rapidly; the closely allied Psoroptes is often seen walking about paired and 
the sexes do not separate when they are killed in alcohol. The current belief 
is that the female orifice for the reception of the male organ is within the anal 
opening; this is a fallacy (see p. 121). I agree with Gudden (1861) and Trouessert 
(1893) that copulation is performed through the minute opening on the 
copulatory papilla, and I believe that the duct which can be traced from this 
opening for a long way into the interior of the body leads to a spermatheca: 
I hope at a later date to deal with the internal anatomy of Sarcoptes and so 
settle this question; at present it is a matter of conjecture. The manner in 
which I believe the male organs are used is as follows. The whole of the 
epiandrium is a thickened part of the body wall; it therefore supplies a fixed 
base for the movement of the other parts. The hyposternite, hinged as it is to 
the hammer heads on each side can only move in one direction and is erected 1 
so that it stands vertically to the surface of the body (or to the plane of the 
paper, in Fig. 16). The erection of the hyposternite would cause the erection 
of the basis penis, for they are locked together by the intromittent spicules; 
there is no difficulty in supposing this, for the basis penis is so attached to the 
body of the mite that clearly it can move in the sagittal plane of the mite, 
and in no other plane. When the hyposternite has been erected so as to stand 
perpendicularly to the ventral surface of the mite it appears probable that the 
copulatory papilla of the female is engaged in the cup-like hollow on the sum¬ 
mit of the outer ring of the hyposternite. This brings the orifice on the papilla 
directly opposite to the tips of the intromittent spicules, which are I believe 
by this device enabled to find the extremely minute orifice. One has further 
to suppose, for I admit that it is a matter of supposition, that the vas deferens 
opens at some point on the summit of the basis penis, and that the spermatozoa 
1 I have failed to produce such erection by manipulating dead males, either freshly killed or 
macerated in water. Anyone who has attempted to manipulate the genital of a creature 225 
microns long will understand why I failed. 
