2Q2 THE INSECTS 



INSECTA. 



The class Insecta has one pair of antennas, three pairs of mouth parts 

 (the fused labium being considered as one pair), and three pairs of legs. 

 They have three divisions of the body head, thorax, and abdomen. 



The head carries the antennas and mouth parts; the thorax, which is divided 

 into the pro-meso and meta thorax, carries upon the ventral surface of each thoracic 

 segment a pair of legs and on the dorsal surfaces of the two posterior segments a 

 pair of wings. The abdomen does not support appendages. The air is supplied 

 by means of tracheae branching breathing tubes which have external openings or 

 stigmata. The tracheae are stiffened by spiral chitinous bands. The Malpighian 

 tubules are excretory organs of the alimentary system and excrete nitrogenous 

 waste material. Insects have two pairs of wings, the second pair of which is fre- 

 quently rudimentary and shows simply as knob-like projections. These are termed 

 halteres or balancers. In some insects both pairs of wings are rudimentary, as in 

 Siphonaptera. 



Where insects show metamorphosis we have voracious worm-like larvas coming 

 out of eggs; these larvae are succeeded by a quiescent nonfeeding encased pupa 

 which finally develops into an imago or fully developed insect. An insect which 

 does not present this developmental cycle shows incomplete matamorphosis. Of 

 the class Insecta only the Siphunculata Rhynchota, Siphonaptera, and Diptera 

 are of special importance. 



SIPHUNCULATA. 

 These are small flat wingless insects not showing metamorphosis. 



The Pediculidse. 



In this family there are no wings and there is no metamorphosis. 

 The acorn-shaped eggs (nits) are deposited on hairs of the host. 



Pediculus capitis. The female is about 1/12 of an inch long; the male smaller- 

 They vary in color according to the color of the hair of the host. The eggs are de- 

 posited on the hairs of the head in number of 6c which hatch out in about six days. 

 The thorax is as broad as the abdomen. The male louse is rounded off posteriorly 

 and shows a dorsal aperture for a pointed penis, while the female is recognized by a 

 deep notch at the apex of the last abdominal segment. There seems to be a marked 

 preference exhibited by lice for their own peculiar racial host. It has recently been 

 suggested that this might account for certain peculiarities in infection where different 

 races were living together and under similar conditions as to food and environment, 

 and yet only one race contracts the disease (beriberi). The head louse has been 

 found to harbor leprosy bacilli when living on a leper. 



Pediculus vestimenti. This louse lives about the neck and trunk and deposits 

 its eggs in the clothing. They number about 75 and hatch out in three or four days 

 and become mature in about two weeks. Unlike the fleas there is no grub stage. 



