The elements of insect anatomy : an outline for the use of students in entomological laboratories / by John Henry Comstock and Vernon L. Kellogg.

  • John Henry Comstock
Date:
1916,
Catalogue details

Licence: Public Domain Mark

Credit: The elements of insect anatomy : an outline for the use of students in entomological laboratories / by John Henry Comstock and Vernon L. Kellogg. Source: Wellcome Collection.

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    Thorax.—The thorax is the second or intermediate region of the body. It is readily distinguished by its appendages ; which are three pairs of legs and two pairs of wings. It consists of three segments ; but as each segment is com¬ posed of several distinct pieces, it requires considerable study to trace the outlines of each segment. We will return to this subject later. Abdomen.—The abdomen is the third or caudal region of the body. The segments of which it is composed are more simple, distinct, and ring-like than those of the other regions. STRUCTURE OF THE BODY-WALL. Chitin. —In studying the anatomy of insects it is found that in the adult stage the greater portion of the body-wall, that part of the insect which corresponds in position to the skin of higher animals, is hard. This hardness is due to the deposition of a horny sub¬ stance, called chitin, in the membrane which constitutes the body-wall. Sclerites.—The chitin is not evenly distributed through¬ out this membrane. Pull the head of a locust so as to sepa¬ rate it from the thorax as far as possible without breaking the skin. Note that the head is joined to the thorax by a soft flexible membrane, in which but little, if any, chitin has been deposited. Examine the sides of the thorax with a lens and observe that the body-wall appears to be made up of many distinct pieces. The integument is, however, really continuous ; and in each case what appears as a distinct piece is simply a por¬ tion of the body-wall in which considerable chitin has been de¬ posited. Such a portion of the body-wall is called a sclerite.* * The sclerites are analogous to the centers of ossification in the bones of the higher animals.
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