i894- 
329 
[Packard. 
different mode of union with tlie head, and tluis phj'siologically 
is turned to an entirely different i)urpose from that of Diptera. 
In the Diptera the maxillae as well as the labium are attached, 
together with the under lip, to the head, by a broad base ; but in 
fleas such a union of the labium with the head is wanting. It is 
nix.p 
Fig. U. Head of Pulex canis $ ; I, au area on middle of the side 
of 1st abdominal segment in $ and V » covered with numerous very fine 
appressed hairs. 
articulated by a firm, brown, chitinous piece in the median line of 
the under side of the head, and this union is so loose that it has 
been doubted whether the Sarcopsyllidae have a complete labium. 
It forms, in this group, however, in its basal portion, not the 
sheath for the piercing apparatus, but has only a rather shallow 
furrow, which in the anterior section of the beak where the trunk 
of the stem, of the labium divides into the paired palpi, at least in 
Pulex, forms two flaps, laterally enclosing the puncturing organs. 
''But the maxillae act vicariously (and herein lies a fundamental 
difference from the dipterous type), in the lack of protection by 
the base of the sucking tube. They arise as two broad plates on 
each side of the head, and protect not only the components of 
the puncturing apparatus, but also the base of the under lip." 
