THE PHYLA ARTHROPODA AND ONYCHOPHORA 



segments, as in most other insects. In tlie locust the anterior wings are 

 usually heavy and tough and function as protective covers for the delicate, 

 membranous metathoracic wings. In the lubber locusts both pairs of wings 

 are greatly reduced, with a corresponding decrease in the power of flight. 

 The wings of insects are composed mainly of exoskeleton, with a very small 

 amount of cellular material between the upper and lower skeletal layers. 

 They are stiffened and supported by thickened structures, called "veins," 

 between which the wing is thin and membranous. The veins also mark the 

 pathways of channels through which blood circulates. 



The abdomen lacks segmental appendages, and none appears in this region 

 during development in the locust; in certain other insects there are traces of 

 vestigial abdominal appendages in the embryonic stages, and these persist to 

 adulthood in some small, wingless, primitive insects. In the female locust a 

 large ovipositor is present at the posterior end of the abdomen, surrounding 

 the external opening of the female reproductive system. In the male an 

 eversible penis marks the opening of the genital duct, just ventral to the 

 anal opening at the tip of the abdomen. 



External openings of the respiratory system appear as the paired spiracles; 

 one lies on each side of every thoracic segment and each of the first eight 

 abdominal segments. In life, the spiracles are opened and closed rhythmically 

 with the breathing movements of the body. The so-called tympanic membranes, 

 which are the external parts of the auditory organs, are conspicuous structures 

 like eardrums on the dorsolateral portions of the first abdominal segment of 

 the locust. 



^^K 



1^ '^^c^fo'^ 



loo 



Fig. 15.17. Mouth parts of a locust 

 (.Adapted from T. Dobzhansky, Evolu- 

 tion, Genetics, and Man, copyright 1955 

 by John Wiley and Sons, Inc., printed 

 by permission.) 



Labrum 



Labium 



447 



