OF WASHINGTON. 425 



Pediculidae there is no trace of wings, and their loss may have 

 been due to parasitism ; but there are many non-parasitic 

 Hemipterous insects that have shortened wings, the short-winged 

 forms often occurring in species normally fully winged. The 

 Mallophaga are also wingless, but they have their most nearly 

 related species in the Psocidaa, which present many examples of 

 rudimentary wings. 



The legs present numerous examples of modification, the most 

 striking being structures adapting the species to clasping the 

 hairs or attaching themselves to the bodies of their hosts. 



Melophagus presents a highly developed clasping organ in the 

 tarsus. The Pediculidae have the tarsi short and opposing the 

 end of the tibia, but the basal joint and the claw present corru 

 gated faces to add to the rigidity of hold, and in Ifcematopinus 

 sui's there is a protractile disk on the end of the tibia which, when 

 forced outward, presses on the hair and doubtless is used to 

 strengthen the hold on the hair. This structure very likely occurs 

 in other species as well, but it is not easily seen in dry or prepared 

 specimens. 



The Mallophaga present two forms of legs the one short in 

 tarsus and with the claw fitting against the end of the tibia as in 

 the Pediculidae, the other long and fitted more for running than 

 for clasping. 



In the ticks and mites there is a great variety of structure in 

 the legs, and the modifications of clasping and adhering organs are 

 quite complex. The tarsi are often, in addition to the claws, pro 

 vided with suctorial disks or sack-like organs, the purpose of 

 which is evidently to assist the creature in adhering to its host; 

 but in addition there are, in some species, notably Symbiotes 

 bovis, suctorial organs located on the different parts of the leg, so 

 that at almost every point the animal can make use of a sucker to 

 ensure its attachment to its host In Uropoda there is an umbili 

 cal thread which is partly excrementitious and which fastens tc 

 the host by a broad adhesive disk. In many cases the mouth- 

 parts serve as organs for the attachment of the individual as well 

 as for obtaining food, so that the means of adhering to the hosl 

 animal are made very complete. 



The genital organs have not, in general, undergone any very 

 striking modification, though there are in some instances adapta 

 tions for clasping during the copulatory process. 



