Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25760/898/
INSECTA. 
390 
the maxilla and galea seems more peculiarly 
adapted to the phytophagous feeders, since in 
the true carnivorous insects, Cicindelida, tiger- 
beetles, and the larger Carabidæ, ground-bee¬ 
tles, the maxilla is more elongated, the inter¬ 
nal lobe, or apex of the lacinia, is more acute, 
and often armed with a sharp hook, and the 
galea assumes the form of a distinct palpus, 
shorter but similar in appearance to the true 
maxillary palpus. This is more manifestly 
the case in the tiger-beetles, in which the galea 
is a distinctly double-jointed palpus, placed 
on a feeler-bearer, and the lacinia is armed 
with a long sharp hook, evidently more adapted 
for seizing and piercing its living food, like the 
canine teeth of carnivorous quadrupeds, than 
for comminuting it like the strong tuberculated 
galea of the vegetable-feeding Melolontha, or 
the tuberculated teeth of herbivorous quadru¬ 
peds. The office then of the galea, in dis¬ 
tinctly carnivorous insects, is simply that of a 
palpus or feeler, and in accordance with this 
view we find that in the tiger-beetles it is 
longer than the inferior lobe, or hooked por¬ 
tion of the lacinia. In the ground-beetles 
Mr. Newman has remarked that it is shorter 
than the lacinia, but, in the generality of the 
tribe, we have also found it longer, as in the 
rapacious Cicindelidæ, particularly in the lar¬ 
ger Carabidæ, and this is also the case in some 
of the Harpalida, particularly in one species, 
Zabrus gibbus, which is known to be a vege¬ 
table feeder. This form of the galea, however, 
seems more peculiarly to belong to the carni¬ 
vorous insects, as it is also found in the Dyti- 
cidæ, but not, as we have seen, in the nearly 
allied but far less rapacious Hydrophylida. 
On the other hand, in most insects which feed 
entirely on vegetable matter, the galea is of a 
more obtuse form, and is less distinct from the 
other parts of the maxilla than in the rapacious 
insects. Thus in the greater number of the 
true vegetable feeders the galea is short, thick, 
and densely covered with hair. This is the 
case not only with the maxillæ, but also with 
the mandibles in those insects whose food is 
the pollen and perhaps also the honey of 
flowers, as in the Cetoniidœ, and also in the 
Geo trap Ida and other Scarabœidæ, which feed 
upon soft decaying vegetable matter. In the 
Cerambycidœ, as in the rare insect Monochamus 
sartor ,* in the Lepturida, which are found 
upon umbelliferous plants feeding on the pollen 
and honey; and in the stag-beetle, Lucanus 
cervus, which subsists on the sap that flows 
from the wounded bark or roots of trees, the 
galea is always densely covered with hair, and 
sometimes elongated to a considerable extent, 
as in the stag-beetle. In those species which 
are purely phytophagous, as many of the 
Galerucida and Chrysomelidæ, which feed on 
the parenchymatous structure of leaves, both 
the galea and lobus inferior are short, obtuse, 
and covered with stiff hairs,while in the Coccine/- 
lidœ that very much resemble the latter insects, 
but are carnivorous feeders, the galea is longer 
and distinctly jointed, and resembles the same 
part in Hydrous, being still covered with hair. 
* Curtis’s British Entomology, pi. 219. 
This is also the case in the common meal- 
beetle, Tenebrio molitor, which belongs to a 
family of less distinctly vegetable feeders. 
From these facts we are inclined to believe 
that the structure of the maxilla has much 
closer connexion with the kind of food and 
habits of the insect than that , of either the 
labium or the palpi. The latter organs, how¬ 
ever, are subject to great variation in the form 
of the terminal joint, which in some species is 
much dilated and shaped like a hatchet, as in 
the common lady-bird, Coccinella, while in 
others it is acute or obtuse. The number of 
joints is usually four, and it has been sup¬ 
posed that there are never more, either in the 
maxillary or the labial palpi, in any Coleop¬ 
terous insect, but the Rev. Mr. Kirby* has 
mentioned an instance in which there appeared 
to be an anomalous condition of the maxillary 
palpi, in this respect, in one of the Geode- 
phaga, Sericoidia bembidioides, K. In one of 
the palpi in this insect there was a fifth joint, 
retractile within the fourth. Mr. Kirby sug¬ 
gests that since the fifth joint was not apparent 
in the other palpus, it may perhaps have been 
a false joint, produced by an effort of nature 
to repair a mutilated organ, but at the same 
time observes that if this were the case it is 
the only instance he has met with in true in¬ 
sects of the reproduction of a lost organ. 
The antenna, constitute the remaining move- 
able parts of the head (fig. 369, a). They are 
occasionally absent in the larva, but never in 
the perfect state in any insects. They are two 
jointed organs, attached to the head by a dis¬ 
tinct and freely moveable articulation, in some 
insects near the middle of the front part of the 
head, but in Hydrous and most Coleoptera 
on each side immediately anterior to the cor¬ 
neae, at the extremity of the epicranial suture, 
but never, so far as we are aware, in the epi- 
cranium itself. They are subject to much 
diversity of form, on which account they have 
been employed by naturalists as affording cha¬ 
racteristic distinctions of different families. 
They have been divided into several parts, only 
three of which appear to be generally applica¬ 
ble. These are the scupus, (fig. 371, m 1 ), pedi- 
cella (2), and clavola (3).f The scapus, or 
basial joint, is usually very long, and often the 
most conspicuous part of the antenna. It is 
connected with the tondus, or part upon which 
it moves, by means of a ball and socket arti¬ 
culation, beneath the external margin of the 
clypeus. The second joint, pedicella, in Hy¬ 
drous, as in almost every species, is a minute 
and nearly globular articulation, which allows 
of the freest motion, and supports the re¬ 
maining portion of the antenna, the clavola, 
which forms the chief part of the organ, and 
is that which varies most in general structure. 
When each succeeding joint of the clavola is 
gradually diminished in size from the base to 
the apex of the organ, as in the Gryllidæ, 
Achetidæ, and Blattidœ, fig. 342 and 343, the 
antenna presents its simplest condition, and is 
* Fauna Boreali-Americana, vol. iv. Insects, 
page 15. pi. i. fig. 2. 
t Kirby and Spence, p. 515, et seq.
        

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