HUNGERFORD: AQUATIC HEMIPTERA. 239 



phamyx, while the other, situated on the ventral side, is the 

 "canal of execution" (outlet of salivary glands.) 



With the Corixids the intake canal is relatively large, al- 

 lowing the ingress of large solid particles. 



Internal. 

 The oesophagus, as shown on plate XXX, is slender as in 

 other Hemiptera, but the mid-gut is large, accommodating a 

 considerable quantity of food. The length is not strikingly 

 greater than that of other bugs, such as Notonecta. The 

 slender oesophagus enlarges to form the oesophageal valve, 

 and the tract greatly enlarges to form a series of pouches. 

 It then narrows slightly to form a more even cylinder. At 

 about the level of the fifth abdominal segment it turns to the 

 right and folds forward to near the front margin of third 

 abdominal segment, where it makes a dorsal turn and bends 

 caudad in nearly a straight line to the anus. The mid-gut ter- 

 minates shortly before the last bend, as indicated by the at- 

 tachment at this point of the four Malpighian tubules. An 

 elastic walled rectal pouch is present, on the dorsal wall of 

 which terminates the Malpighian tubules. 



STUDIES RELATING TO THE FOOD OF CORIXIDS. 



Object and General Plan. 



Having determined the source of the food supply of the 

 boatmen, there yet remained the question of the exact nature 

 of their forage. The results herein presented have been gath- 

 ered from experiments to determine the usual and essential 

 diet of these peculiar bugs. A solution of this problem has 

 been attempted by feeding the insects upon surveyed mixed 

 cultures and upon pure cultures. The former to indicate the 

 existence of selection in their foraging, and the latter to deter- 

 mine if possible the essential organisms of their diet. 



Thus the body of this paper consists of a report of the {a) 

 history and diagnosis of the culture, {h) its survey, and (c) 

 an analysis of stomach contents of Corixids after living within 

 the cultures. 



Technique. 



In order to use due care in the manipulation of the ma- 

 terials the following precautions are observed: A given lot 

 of boatmen of some species is selected and placed in clear 

 water for a time, to remove from their bodies any foreign 



