Thorax in winged Insects. 153 
Ishall take another opportunity of discussing the external structure of 
the 4rachnida, which remains as yet quite unknown. Ishall merely 
now state that the 4caride are those in which the segments of the body 
are most condensed or confluent, as the Macrourous Crustacea are those 
Annulosa which appear in the imago state to offer the greatest regular 
developement. A Scolopendra offers a construction which goes appa- 
rently beyond the regular type, and thus such Ametabola are in zoology 
natural monsters.* The larve of winged insects have in general thir- 
teen segments, indeed I know at present of no one exception. A cater- 
pillar, for instance, has a head, three segments for the thorax, and nine 
for the abdomen. The first three thoracic segments carry feet; the seg- 
ment immediately following, or the fifth of the thirteen, (which, as I 
conceive, may in general be accounted to belong to the abdomen of in- 
sects,) rarely possesses locomotive appendages,t+ but the next segment to 
this, that is the sixth segment (reckoning the head as one), is supplied 
with them in certain larve, such as those of some Tenthredinide, which 
have twenty-two feet. The last seven abdominal segments very often 
one or other carry spurious feet; and on the other hand, the body may be 
quite vermiform,+ that is without any feet whatever, as we know from 
looking at the larve of certain Hymenoptera, Coleoptera, and Diptera. 
behind the rest of his work. Scarcely a word, for instance, is said respecting 
the class of Crustacea, and yet some account of their forms appears absolutely 
necessary in an Introduction to Entomology. 
* Understanding well that every one of the thirteen primary segments of an 
insect, when at the perfection of developement, is divisible, as will be shewn 
in the following pages, into four minor segments, we get fifty-two segments 
for an insect that is perfectly regularly developed, and this is the maximum 
number in Chilognatha. The Chilopoda have only about half this number of 
segments, owing to their primary segments in general being only about half as 
much developed as those of the Julide. 
+ In Crustacea, however, the fifth segment of the thirteen very commonly 
carries feet, or locomotive appendages, 
t In the “ Hore Entomologice” 1 followed the three greatest naturalists that 
England has produced, Ray, Willughby, and Lister, in placing certain Vermes 
among the Annulosa, A minute and careful examination of this subject has 
convinced me of the accuracy of this mode of viewing nature. 
