LOCUSTS .4yD GRASSHOPPERS (ACRIDIID.E). 85 



with the air by a row of spiracles, or air-holes, or breath- 

 ing-holes (stigmata), in the sides of the body. Acridiidae 

 are remarkable amongst the Orthoptera for the possession 

 of air-sacs or vesicular dilatations in the interior of the 

 body in connection with the tracheae. Many winged 

 insects possess such vesicles. In bees, wasps, moths 

 and butterflies, flies, and in some beetles, and some bugs, 

 they are found well developed, being most numerous 

 and capacious in volant insects which sustain the longest 

 and most powerful flight. But in the larval or immature 

 forms of these they do not exist, nor do they occur in 

 truly apterous insects. In the flying locusts they are as 

 numerous and as large as in any group, more numerous 

 perhaps than in the bee in proportion to the body, 

 while certainly there is a greater number of large sacs, 

 and both sexes are equally well provided. Packard 

 describes the distribution of these remarkable elastic 

 sacs in the Rocky Mountain Locust. There is a 

 thoracic set, consisting of a pair of very large size, 

 with which are connected some smaller ones in the 

 head ; and an abdominal set. The last are very extra- 

 ordinary, being of such large size that they may be 

 regarded as only becoming fully expanded at a time 

 when the body being comparatively empty, food being 

 wanting, there is no normal distention of the alimentary 

 canal, and the other contents of the body are as yet 

 undev^eloped. Although according to one observer they 



