Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Todd, Robert Bentley
always accompanies that of the trachea. The 
crura vary much in length in different species. 
In Neuroptera, Hymenoptera, Lepidoptera, 
Diptera, and Homoptera they are short and 
thick, and form with the medulla a thick collar, 
through which the oesophagus passes as a narrow 
tube; but in the Gryllidœ (fig. 410), and 
more particularly in the Lucanidte (fig. 413), 
they are excessively elongated, and they are 
also of great length in the Timarcha. The 
medulla oblongata varies much in size ; in some, 
as in the Lepidoptera, it is as large as one of 
the lobes of the cerebrum, while in others it is 
scarcely thicker than the crura. It is always 
largest where large nerves are required for the 
parts of the mouth, which in all cases are 
derived from it. In this respect there is a striking 
analogy between it and the medulla oblongata 
of vertebrata. The anterior pair of nerves from 
this part are given to the labium and lingua, 
while the two next pairs are given to the man¬ 
dibles and maxilla. In the distribution of these 
nerves there is great similitude to that of the 
fifth pair in the higher animals. In the larva 
state these nerves are always distinct from each 
other, but in the perfect they are often united 
at their base into one trunk. This is the case 
in the Timarcha and Gryllidœ. The anterior 
pair is the largest in mandibulated insects, 
and supplies the powerful mandibles, while 
the posterior pair is given to the maxillæ. The 
union of these nerves at their base is interesting 
from the circumstance that during manducation 
a consentaneous movement of these parts is 
required, since, while the mandibles are em¬ 
ployed in chewing, the maxillæ are also em¬ 
ployed in turning and assisting to pass the food 
into the pharynx. In the Sphinx ligustri, and 
other Lepidoptera, the chief portion of the man¬ 
dibular nerve has disappeared in the perfect 
state, in consequence of the atrophy which has 
taken place in the mandibles during the trans¬ 
formations ; but one branch of the nerve which 
exists in the larva state appears to have become 
approximated to the maxillary nerve, which is 
now greatly elongated and given to the pro¬ 
boscis, the representative of the maxillæ of 
the larva. The branch that appears to have 
belonged to the mandibular nerve is extended 
along the concave or inner side of each half of 
the proboscis, where the sense of taste may 
justly be suspected to reside, and is traceable 
very nearly to the extremity of the organ, where 
the papillae we formerly noticed are situated, 
and in the direction of which this nerve is 
extended. From this we believe it to be 
analogous in function to the gustatory portion 
of the fifth nerve in vertebrata. In Lucanus 
cervus the mandibular nerve is of great length, 
and is so extensively developed as to afford 
almost a proof of the elongation of nerves 
during the metamorphoses of the insect. We 
have traced this nerve from its origin (fig. 
413, c) into the base of the mandible, which it 
enters a little external to the insertion of the 
flexor muscles, where it is divided into three 
trunks, the inner one of which we have traced 
very nearly as far as the apex of the mandible. 
The other two are situated more externally. 
Fig. A\Z. 
^ (1 
Nervous system of Lucanus cervus. 
A, the brain ; B, optic nerves ; C, sympathetic ; 
D, antennal nerves ; a, ganglion of the vagus 
nerve ; b, the nerve ; *, its division on the oeso¬ 
phagus ; d, nerve to the first pair of legs ; f, 
nerve to the wings, giving off at its base a small 
nerve to the elytra ; g, nerve to second pair of 
legs ; k, to third pair ; l, abdominal cord and 


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