THE ABDOMEN. 25 



those insects in which the abdomen is entirely of a 

 horny texture^ and in these each segment is often seen 

 to be composed of two half rings^ one placed npon the 

 back, the other on the belly, and united at the sides 

 by a soft membrane. This structure enables the 

 abdomen to expand and contract, a movement which 

 is essential to respiration. In many of those insects 

 whose anterior wings are converted into horny sheaths, 

 the abdominal segments are firmly united together 

 in their lower or ventral portion, forming a single 

 strong horny plate ; but to make up for this, the upper 

 surface of the segments is entirely covered with a 

 flexible skin, which, when concealed beneath the wings 

 and elytra, is, of course, protected from all danger. 



At the apex of the abdomen will be found, some- 

 times concealed within the last segment, sometimes 

 projecting from it, a variety of appendages connected 

 with the generative organs. The most prominent of 

 these, and in the present case there is no necessity 

 for our paying any attention to any others, consist in 

 the males of a variety of clasping organs, whilst the 

 females are often provided with wonderfully ingenious 

 instruments for depositing their eggs in proper situa- 

 tions. The latter will come in for a fall share of our 

 notice hereafter, so that any further reference to them 

 here would be out of place. 



Internal anatomy. — The reader may probably think 

 that too much space has been devoted to the investi- 

 gation of the external skeleton of insects, and that 

 these dry bones would be all the better for having a 

 little flesh upon them. He will find, however, that 

 for our present purpose, the dry bones are of more 

 importance than the flesh, and although the examina- 

 tion of the internal anatomy of these creatures is 



