Pack;ir(l.] 324 [^»y 2, 
yet as seen in Figs. 4 and 5 it ends in six long slender si»inules, 
the three on eacli side slightly diverging from the three on the 
other. Its shape when carefully worked out wall jn-obably be 
found to be not much unlike that of the labium of Dixa (Fig. 
8), Simulium and Tanj'pus (Fig. 7). 
Except in the form of the labrum, and the general vermiform 
appearance of the body, the larva of the Siphonaptera does not 
externally closely resemble the shape of the dipterous larvae, 
though indeed as much like them as those of any other metabolic 
order of insects. 
Internal anatomy. — It is to be noted that in the freshly 
hatched larva of Palex canis both the brain and infraoesopha- 
geal ganglia are contained within the head. 
Brauer attaches great importance to the position of the brain 
in dipterous larvae, remarking: "As hereditary and typical for 
the entire great group of dipterous larvae appears to be the 
position of the head-ganglia, whether they lie in a head-capsule, 
or are free, situated far behind the mouth-opening, or directl}' 
behind the maxillary capsule which supports the mouth-parts and 
encloses the oesophagus" (p. 4). He then mentions as one of 
the most important characters of the Diptera eucephala, the fact 
that the first ganglion (brain) is contained in a completel}^ differ- 
entiated head.^ 
We see (Fig. 1) that in the larval Pulex not only is the head 
itself more perfectly formed than in any dipterous larva, but also 
both the brain or supraoesophageal, and the infraoesophagcal, 
ganglia are contained within the head. It is, however, possible 
that later on in larval life they may move backwards and lie partly 
within the segment next behind the head. 
The absence of salivary glands is another point in which the 
larvae of the Siphonaptera differ from those of the flies. 
' Osten Sacken criticizes this statement of Brauer, remai'king tliat it need? confirma- 
tion, and he refers to tiie statement of ^liall and Hammond that tlie larval head of 
Chironomns "contains no brain," althouj^h this genus belongs to the Eucephala. 
(Berlin, ent. zeitschr., 1892, p. 445,403.) Comjiare also the work of Weismann, Die eut- 
wicklungderdipteren, 1863, wherein is figured the brain or 1st ganglion of Chirononuis, 
which in the embryo is situated ))ehind the head and even behind the prothoracic pair 
of false legs, though the head is as wide as the body. (Taf. 4, lig. 44, 40, 'i I.) 
Miall also states (Trans, ent. soc. Lond., 1893, p. -241) that in the larva of a tipulid 
fly, Dicrnnota bimaculnfn, "none of the ganglia lie in tin- head. The brain, willi tin- 
suboesophageal and prothoracic ganglia, lies in tbe f^ri' part of the mesntluirax ; Ibe 
mesothoracic ganglion occupies tin- hinder jiait oi thf s;inie si'<;nu'ut." 
