162 ALEXANDER PETRUNKEVITCH 



The midgut may easily be recognized because of the presence 

 of a cardiac valve, because of its thin walls and, further, because 

 it is still filled with embryonic yolk. It has the appearance of 

 a wide tube with larger lateral branches or diverticula usually 

 known under the name of 'hver.' The anterior portion of the 

 midgut proper runs at almost a right angle to the longitudinal 

 axis of the body and belongs to the cephalothorax because it 

 lies in front of the diaphragm. Its posterior end extends only 

 to the end of the fifth abdominal segment. The diverticula 

 of the midgut extend forward almost to the anterior end of the 

 cephalothorax and backward through the entire preabdomen, 

 the last dorsal diverticulum reaching even into the first post- 

 abdominal segment. The gross anatomj^ and segmental arrange- 

 ment of the diverticula are not easy to understand. Sagittal 

 sections show a clear separation of the diverticula into ten 

 metamerically arranged groups, two of which are in the cephalo- 

 thorax and eight in the preabdomen. Their metameric nature 

 is especially emphasized by the dorsoventral muscles and the 

 hypocardiac ligaments. The ligaments shoTNTi in text figure 

 A as ventral projections of the heart exist only in the preabdomen. 

 Of the muscles, one pair is in the cephalothorax where they are 

 attached by one end to the carapace between the two cephalo- 

 thoracic diverticula and by the other to the endosternite above 

 the nervous system. There are eight pairs of dorsoventral 

 muscles in the preabdomen passing between the diverticula, 

 right and left of the midgut, from the back to the ventral sur- 

 face of the body. The first pair is easily overlooked as it lies 

 closely apphed to the posterior surface of the diaphragm. Dor- 

 sally, these muscles are attached to the anterior end of the first 

 abdominal tergite on the outside of the epicardiac ligaments. 

 Ventrally, they are attached, hke the cephalothoracic pair, to 

 the endosternite above the nervous system. All other dorso- 

 ventral muscles are attached at both ends to the chitin of the body 

 wall. The dorsal attachments are to the outside of the epicardiac 

 ligaments. The ventral attachments are slightly farther apart 

 than the dorsal, one pair for each abdominal sternite, the second 

 pair lying at the sides of the genital opening, and the third 

 at the sides of the basal plate of the comb. 



