190 



be cousidered a si)ecializatioii to meet the x't^t^uliar eiiviroumeut they 

 have adopted. 



The specialized structure ofteu seen iu the euhirg'ed third Joint in the 

 males of Lipeurus and some others, and wliich 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 fuuctiou with the 

 copulatory process. 



A ijeciiliarly toothed process on the nasal joint in the- female Hcema- 

 topimis 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 maxillne are modified in both Psocidie and 

 Mallophaga, and in the Philopteridie have a further loss of the palpi. 



The labium, which forms nsually a quite conspicuous object iuMallo- 

 l)haga, is remarkably similar to that in Atropos, in some cases even the 

 rudimental palpi being present. In the Pediculidie, 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 Liotheidiv and Philopteridie (excepting the 

 aberrant Gyropus), these in Liotheidoe being composed of a short basal 

 joint and a larger second joint with usually two articulated claws. In 

 the Philopteridie 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 s])ecialized and while much bet- 

 ter for the insect in its usual l(>cation 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, iu Gyropus is such that it is not imi^ossi- 

 ble that the Philopterid form could be derived from the Liotheidae, 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 ;i generalized Mallophagau than any 

 Philopterid. 



The difference in habit accompanying this difference in structure is 



2 Bull. 7, Div. Entomology, U. S. Dept. Agriculture, p. 25. 



