34 THE AMERICAN NATURALIST. [Vor. XXXVI. 
it is the sternum of the cervical segment which has migrated 
cephalad and become a part of the skull. In Corydalis the 
sternellum of the cervical segment is retained back of the gula 
(Fig. 5, Sz). 
Although the maxilla are well-developed organs, the maxil- 
lary segment itself is greatly reduced. The most conspicuous 
element of it is the lingua, the unpaired portion of the hypo- 
pharynx. This, as has been shown (Fig. 8, 7), arises between 
the rudiments of the maxilla and evidently pertains to the 
sternite of this segment. 
The opening of the salivary glands is in thelingua. Carriére 
has shown that these glands arise as the spiracular invagi- 
nations of the prothorax, and that their openings migrate 
cephalad, and towards each other, finally forming a single open- 
ing in the lingua (Carriére and Bürger, 97). This explains the 
absence of spiracles in the prothorax, and is one of the most 
remarkable instances of the migration of organs and change 
in function yet described. 
Regarding the maxillary pleurites of the completed head, 
almost nothing has been published. Huxley, in his descrip- 
tion of the structure of the cockroach (78), stated that the 
cardo of the maxilla is articulated ** with a thin skeletal band 
which runs round the posterior margin of the epicranium." He 
made no suggestion regarding the homology of this sclerite ; 
and subsequent writers do not appear to have done so. 
This lateral band (Fig. 4, m.em.) is one of two sclerites, 
between which is the invagination which forms the posterior 
arm of the tentorium ; the other of these two sclerites, the 
anterior one, is much more reduced than this one, still it can 
be seen in Periplaneta and in Gryllus. The articulation of 
the maxilla is at the ventral end of these sclerites just ventrad 
of the invagination between them, the open mouth of which is 
very conspicuous in the more generalized insects. 
The relation of these parts corresponds exactly with what 
exists in a thoracic segment, where each leg is articulated 
just ventrad of the lateral apodeme, which is an invagination 
between the episternum and the epimeron. Evidently the band 
described by Huxley is the epimeron of the maxillary segment, 
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