1918] Alimentary Canal of Altica Larva 285 



the mesenteron which runs caudad and the ileum which runs 

 cephalad, is formed a U-shaped bend, on the inner side of which 

 the bladder opens. Having bent forward, the hind intestine 

 extends as far cephalad as the posterior edge of the fifth 

 abdominal segment, where it turns back on itself; this bend 

 marks externally the separation between the ileum and colon. 

 The colon, which is nearly straight, runs caudad as far as the 

 anterior edge of the ninth abdominal segment, ventrad of the 

 ileum. The colon passes directly into the rectum (third 

 division), which is only one segment long. The anal opening 

 is in the center of the anal proleg, and is shaped like an inverted 

 Y. Macroscopically no difference is apparent between the 

 ileum and the colon. The colon is smaller than the second 

 division of the ventriculus; anteriorly, the colon is of the same 

 diameter as the ileum, but it gradually increases in size poster- 

 iorly. The rectum is surrounded by powerful circular muscles, 

 which show up clearly in a dissected specimen, and clearly 

 differentiate it from the rest of the alimentary canal. 



The structure of the different regions of the alimentary 

 canal is discussed in the remainder of this paper. The parts 

 are considered in order, beginning at the anterior end. 



2. THE HISTOLOGICAL STRUCTURE OF THE 

 ALIMENTARY CANAL. 



The Fore Intestine, 

 the mouth-parts and their muscles. 



Mouth parts. The mouth parts of the larva of the alder 

 flea beetle consist of the typical biting pieces; a labrum, two 

 mandibles, two maxillae, and a labium. The writer has already 

 published figures of these structures (Woods 1917, Fig. 19). 



Cuticular invaginations. There are four cuticular invagi- 

 nations in the head of this larva, one unpaired and three paired, 

 which serve for the attachment of muscles. The unpaired 

 cuticular invagination extends along the mid-dorsal line of 

 the head from the caudal margin of the epicranium as far 

 cephalad as the clypeus. Both primary and secondary cuticulae 

 are equally involved. The paired invaginations arise from the 

 labrum, the mandibles and the maxillae. 



