Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Todd, Robert Bentley
rate, and the genital organs, slow in their 
development, are highly complicated in the 
perfect state. These animals generally pass 
through a series of metamorphoses, and throw 
off their exuvial covering five or six times 
during their development. This class is the 
most numerous in the animal kingdom, com¬ 
prehending about a hundred thousand species. 
The greater part of their life is spent in the 
larva state, during which they are generally most 
voracious, like the young of other classes. In 
the adult state the masticating organs and the 
digestive apparatus vary much according to 
the kind of food in the different species, as is 
seen in comparing the alimentary canal of a 
carnivorous cicindela campestris (Jig. 37.) with 
Fig. 37. 
that of a phytophagous melolontha vulgaris, 
(fig. 38.) In the carnivorous insect (fig- 37.) 
the intestine passes nearly straight through the 
body with few enlargements in its course, and 
the glandular organs have a simpler struc¬ 
ture. The oesophagus passes down narrow 
from the head, and dilates into a wide glandu¬ 
lar crop (a), which is succeeded by a minute 
gizzard, and this is followed by the chylific 
stomach (b, c), which is covered like the crop 
with minute glandular cryptæ or follicles. At 
the pyloric extremity of the chylific stomach, the 
liver, in form of simple biliary ducts, pours its 
secretion into that cavity by two orifices on each 
side (d). The short small intestine (e) opens into 
a wide colon (f), which terminates in the anus 
(g). In the vegetable-eating insect, (fig. 38) 
the alimentary canal is more lengthened, con¬ 
voluted, and capacious, with more numerous 
dilatations, and the glandular organs are more 
developed. The crop (a) of the melolontha is 
Fig. 38. 
succeeded by a minute rudimentary gizzard, and 
to this succeeds a long and sacculated glandu¬ 
lar or chylific stomach, which becomes narrow 
and convoluted below, and terminates in a 
small pyloric dilatation, which receives the 
four terminations of the biliary organs. The 
succeeding part of the intestine is also con¬ 
voluted, and has three enlargements in its 
course to the anus (e). The liver (c c) is 
here of great magnitude, and has its secreting 
surface much extended by the development of 
innumerable minute coeea from its primary 
ducts. Insects also often present distinct 
urinary organs, and numerous glands in both 
sexes connected with the organs of generation. 
(See Insecta.) 
12. Arachnida, with the head and thorax 
united, generally four pairs of legs ; with¬ 
out antennæ, or compound eyes, or wings, 
or metamorphosis ; the trunk divided into a 
cephalo-thorax and abdomen ; the head is often 
provided with two pairs of chiliform manduca¬ 
tory organs ; the eyes are simple. The respi¬ 
ration is aerial, sometimes performed by tra- 
cheæ, and sometimes by pectinated pulmonary 
sacs opening on the sides of the abdominal 
surface of the trunk. In their nervous, res¬ 
piratory, and circulating systems they indicate 
a higher grade of development than insects, 
and like them are generally inhabitants of the 
land, attaining considerable size and strength, 
with cunning, cruel, carnivorous habits, and 
often provided with poisonous instruments. 
(See Arachnida.) 
13. Crustacea, with the head and thorax 
generally united, two pairs of antennæ, two


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