349 
[Packard. 
pharynx, and to the pair of large 5-jointed (or 11-13-jointed in 
Vermipsylla) Labial palpi. If this view should be proved to be 
correct, it will tend to show that the Siphonaptera are an order 
parallel and near to the Diptera, but not directly derived from 
them, thougli both may have had a common origin. 
Other Characteristics of the Siphonaptera. 
Absence of a dyjyeus and labriim. — The fleas differ from any 
Diptera, even including the suctorial Pupipara and Braula, in the 
absence of a clypeus and labrutii, while the antennae are inserted 
either above or behind the simj^le eyes. The head is greatly 
Fig. 33. Head of Braula coeca; cl, clypeus; Ibr, labrura; mx, maxilla; 
mx', labium; lb, labellum; ant, antenna. — After Miiggenherg. 
developed in front of the eyes and antennae in adaptation to their 
semiparasitic mode of life and to their peculiar mode of running 
through the forest-like mass of hair of their host, and of taking 
their food. The base of the mouth-parts, being adapted exclu- 
sively for piercing the tissues of their host and sucking blood, are, 
as in the suctorial Hemiptera, inserted or retracted far within the 
head, and there is no need of a clypeus and labrum to brace the 
front part of the head. This absence of a clypeus or hypostoma, 
as well as the absence of vestigial wings and of sternites, suggests 
