190 
be considered a specialization to meet the peculiar environment they 
have adopted. 
The specialized structure often seen in the enlarged third joint in the 
males of Lipeurus and some others, and which in some cases seems well 
adapted to clasping, has very certainly arisen by a gradual increase in 
size of the terminal rim at one point, while their development in the 
males only indicates that they may be connected in function with the 
copulatory process. 
A peculiarly toothed process on the nasal joint in the female Hema- 
topinus antennatus Osborn* is also a case of special structure, the organ 
being apparently connected in some way with a clasping function. 
In the mouth-parts we would naturally expect considerable modifica- 
tion, but for the Mallophaga it is remarkable how closely the Psocid 
structure is retained. The mandibles show no remarkable variation, 
being, perhaps as a rule, somewhat stouter, and the terminal part bi- 
dentate or tri-dentate. The maxille are modified in both Psocidz and 
Mallophaga, and in the Philopteridz have a further loss of the palpi. 
The labium, which forms usually a quite conspicuous object in Mallo- 
phaga, is remarkably similar to that in Atropos, in some cases even the 
rudimental palpi being present. In the Pediculidwe, however, the cor- 
respondence of the oral organs with Hemiptera is obscured, the reduction 
of the rostrum to a one-jointed tubular structure being, if it is homolo- 
gous with the labium of Hemiptera, an extreme of modification. 
Some of the most interesting structures occur in the tarsi, and can 
be unquestionably ascribed to adaptive evolution. In Mallophaga, 
the tarsi present well marked types which form ready means of sepa- 
rating the two families Liotheide and Philopteride (excepting the 
aberrant Gyropus), these in Liotheide being composed of a short basal 
joint and a larger second joint with usually two articulated claws. In 
the Philopteride the tarsi are short, the basal joint thick, and the sec- 
ond joint small, bearing as a rule one claw, which opposes as a rule a 
more or less distinct tibial spur, thus forming a good clasping organ- 
The latter form is evidently the more specialized and while much bet- 
ter for the insect in its usual location renders it practically helpless 
when removed from its host. This difference is so great that with other 
structural differences it suggests the possibility of these two. families 
having originated from independent non-parasitic ancestors. The re- 
duction of the tarsi, however, in Gyropus is such that it is not impossi- 
ble that the Philopterid form could be derived from the Liotheide, al- 
though I do not wish to be understood as suggesting Gyropus as a con- 
necting link between the two families. This genus is a peculiar one, 
presenting some highly specialized characters, and in some respects ap- 
pears to me further removed from a generalized Mallophagan than any 
Philopterid. 
The difference in habit accompanying this difference in structure is 
2 Bull, 4, ie Dawah Wes: ene Agriculture, p. 25. 
