176 PHILIP p. CALVEKT. 



The abdominal muscles are longitudinal and transverse. The 

 longitudinal muscles are tergal and sternal. Of the longitudinal 

 tergal there are two sets : the superior longitudinal tergal abdominal 

 muscles pass from the anterior dorsal part of the tergum of one seg- 

 ment to the same posterior part of the next in front ; the lateral 

 longitudinal tergal abdominal muscles pass from the inferior lateral 

 margin of the tergum of one segment and the adjacent pleural mem- 

 brane to a region somewhat higher up on the tergum of the preced- 

 ing segment. The longitudinal sternal abdominal muscles are quite 

 small, and pass from the anterior part of the sternum of one seg- 

 ment to the posterior part of the preceding sternum. The contrac- 

 tion of the superior tergals of both sides is to extend the abdomen 

 in a straight line, of the sternals of both sides to flex the abdomen 

 ventrally upon itself, while a contraction of the muscles of one side 

 of the abdomen only will bend it towards that side. Transverse 

 muscles occur in the second abdominal segment of the males from 

 tergum to sternum ; and in the spiracle-bearing segments as vertical 

 expiratory muscles (Plateau 11) connecting the terga with the second 

 lateral sternal process, and which aid in the contraction of the ab- 

 domen in the act of expiration. 



THE ALIMENTARY CANAL. 



The alimentary canal is a nearly straight tube running from the 

 mouth on the lower surface of the head to the anus in the rudimen- 

 tary eleventh, or anal segment. It consists of three parts: i\\efore-, 

 the mid-, and the hind-gut. The first and last are formed from the 

 ectoderm of the embryo, like the integument, and have a chitinous 

 lining; the mid-gut is (»f endodermal origin and the chitinous lining 

 is absent. 



The fore-gut (oesophagus and crop) extends from the mouth to the 

 second abdominal segment. Its walls are very distensible, particu- 

 larly at its hinder end. Its only appendages are a pair of salivary 

 glands, which wei'e discovered and described by Poletaiew (9). The 

 glands are compound, and lie in the prothorax. Each acinus is 

 tolerably long and narrow ; their number is greater in the Anisop- 

 tera (above 150) than in the Zygoptera (oO), and in the former 

 group they are more closely bound together by a tracheal net-work. 

 The acini of each gland eventually form a single duct, which dilates 

 into a reservoir, after which it unites with its fellow of the other side. 

 The common opening is on the underside of the hypopharynx, where 



