474 ARTICULATED ANIMALS. 
cular trachea : this, however, as well as the choroid, is wanting in various darkling 
insects ; 3rd, of nerves, which arise from a large trunk proceeding immediately from 
the brain, which there dilates in a reversed conical form, the broad base being towards 
the cornea, and of which the threads, running through the choroid and inner plaster of 
the cornea, terminate separately in each of the facets. There is no crystalhne nor 
vitreous tumour. 
Many insects have, in addition to these composite eyes, simple eyes [ocelli'] , the 
cornea of which is smooth. They are generally three in number, and arranged in 
a triangle upon the crown of the head. In the majority of apterous insects, and 
the larvae of those which gain wings, the ocelli replace the eyes, and are often in- 
serted in a group : judging from the eyes of the Arachnida, they are evidently fitted 
for vision. 
The mouth of Hexapod insects is in general composed of six principal pieces, their 
form being lateral, arranged in pairs, and mostly transversely ; and two others, opposed 
to each other in a direction contrary to that of the preceding, filling up the space be- 
tween the former : one is situated above the upper pair, and the other below the lower 
pair. In the masticating insects, or those which feed upon sohd materials, the four 
lateral pieces perform the office of jaws {mdchoires) , and the two others are considered 
as lips ; but, as we have already observed, the two upper jaws have been distinguished 
by the particular name of mandibles, whilst the two others have alone retained the 
name of maxillae (mdchoires) : the latter are also provided with one or two articulated 
filaments which are called palpi, — a character which is never possessed, in this class, by 
the mandibles. The extremity of the maxillae is often terminated by two divisions, or 
lobes, of which the outer, in the Orthoptera, is termed the galea. We have already 
said that the upper lip is called the lahrum. The other lip, or the labium (levre, pro- 
perly so called), is formed of two parts: the one, solid and inferior, is the mentum ; 
the upper, which often bears two palpi, is the tonguelet (languette), [or ligula]."^ 
In the suctorial insects, or those which derive their food from fluid aliments, these 
different organs of manducation appear under two general modifications. In the 
first, the mandibles and maxillae are replaced by small, setaceous, lancet-like plates, 
forming, by their union, a kind of sucker, which is received in a sheath which takes 
the place of the labium, and is either cylindrical or conical, and articulated, in the 
form of a beak (rostrum), or membranous and fleshy, inarticulated, and terminated 
by two lips (proboscis) . The labrum is triangular and arched, covering the base of 
the sucker. 
In the second of these modifications, the labrum and mandibles are nearly obsolete, 
or extremely small. The labium is no longer a detached piece, and is only distin- 
guished by the presence of a pair of palpi, of which it is the support. The maxillae 
have acquired a very great length, and are transformed into two tubular threads, which, 
uniting by the edges, forms a kind of proboscis which is rolled up in a spiral manner, 
and is named the tongue, but which, to avoid misconception, it would be preferable to 
term the spirignatha : its interior presents three canals, of which the middle one forms 
* According to what I have said in the introductory observations 
upon the Articulata in general, I consider the lower lip to be but a modi- 
fication of the second maxillae of the decapod Crustacea, combined 
with their tongue (languette). The gradual changes which take place 
in the form of these organs, in the Crustacea, Arachnida, and Myria- 
poda, naturally lead to this supposition. In this hypothesis, the six 
thoracic legs must be analogous to the foot-jaws of the Crabs; and as 
has been shown, in the crustaceous genus Apus. Moreover, the five 
anterior abdominal segments of hexapod insects will represent ihe 
segments which bear the true legs in the decapod Crustacea, or the 
third and four succeeding segments of the amphipod and isopod 
Crustacea. The various works published in respect to the thorax of 
insects will necessarily require revision when this part of the body is 
compared throughout the three annulose classes, its nomenclature 
being far from fixed in this respect. 
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