420 Transactions of the Society. 



The Contents of the Abdomen. 



b. Structure. — I shall now make some remarks on the structure 

 found in the abdomen, regarded more especially from the point of 

 view of the microscopist. The containing membranes of the intes- 

 tines, and of the various complicated glands that surround the 

 stomach, are so soluble that they seldom or never show in pre- 

 parations fitted for high powers. However, the following parts 

 are often visible : — (1) the gizzard, or crop ; (2) the rectal papilla? ; 

 (3) the breathing tracheae and the stigmata ; (4) the eggs or larvae 

 or pupa ; and (5) receptacula seminis or spermathecoe. 



1. The gizzard is an elaborate and interesting structure in 

 many insects. In our large grasshoppers it is scarcely a micro- 

 scopic organ ; in the earwig (Forficula) it consists of two arms 

 studded with rows of sharp hooks ; in the cockroach (Periplaneta) 

 it is, though chitinous, more muscular and is adapted for crushing, 

 not tearing. All can be easily found in preparations. Nothing 

 similar exists in the flies, but an organ composed of a number of 



a. Papilla. b. Receptaculurrit 



Fig. 114. — Rectal papillae of Hydrellia griseola Fin. 9 . Theldelicate membrane 

 is the anal extremity of the intestine. In the process of dissection it has been 

 forced out of the anus, and consequently reversed ; normally, the apices of the 

 cones of the papillae are on the inner side, but I have drawn it just as I saw it. 

 This figure also shows the single receptaculum seminis that is found in this fly, 

 which, moreover, is remarkable, as the mouth contains a complete maxilla. 



filaments, springing from a central tube, is often met with in the 

 calyptrate Muscidoe. This is the chyle stomach. The crop or 

 gizzard can be differentiated in the blow-fly (Calliphora), though 

 to see it special dissection is necessary ; it is not likely to appear 

 in preparations, such as the other observations can be made from. 

 A somewhat similar organ is found in the abdomen of the fleas 

 (Pulicidoe). 



2. The rectal papillae will often be met with pressed out of the 

 anus. In some Diptera they have minute scales ; this is most 

 marked in the Dolichopodida:, the " fan-tailed flies," where micros- 

 copists will find them mostly in the abdomen or in the ovipositor. 

 I give a figure of them as they are found in a minute Ephydrid, 

 Hydrellia griseola Fin. This was drawn from a dissection : it is 

 seldom these organs appear so clearly. 



3. The tracheae are often dissolved away by the potash, but 



