GASTRIC C.ECA OF THE HETEROPTERA. 115 



istic in form that they could readily be recognized in mixed 

 cultures. 



Since all possibility of checking the cultures by infection experi- 

 ments had to be definitely abandoned, there was very little 

 inducement, at least at first, to attempt the cultivation of these 

 bacteria from the Coreidae or from such lygaeids as Blissus leucop- 

 terus, in all of which they are short, uniform rods with nothing 

 morphologically to distinguish them from dozens of other sapro- 

 phytic bacteria that might occur as contamination in the cultures. 

 While these insects appeared wholly unsuited for preliminary 

 culture tests, many of the Pentatomidae, as Peribalus limbolarius, 

 Brochymena quadripustulata, and especially Miirgantia histrionica 

 were apparently ideal for this purpose, as the bacteria which they 

 harbor, instead of being the small, typical bacillus form of the 

 Coreidae and of most of the Lygaeidae, are very characteristic in 

 appearance, varying from the extremely long, straight, rod-like 

 forms of Peribalus through the short, uniformly bent organisms 

 of Brochymena to the remarkably large, characteristically con- 

 torted form uniformly occurring in Miirgantia. 



For this apparently good reason, the culture work was, at 

 first, concentrated especially on Miirgantia histrionica and a few 

 other pentatomids; for it was very clear that if the caecal bacteria 

 from these insects would develop on artificial media at all, and still 

 retain the characteristic form as they occur in the caeca, there 

 would be no difficulty whatever in differentiating them from any 

 possible contamination that might appear. 



In the larger Heteroptera, as well as in those of moderate size, 

 it was found that by careful dissection any division of the ali- 

 mentary canal could be removed with practically no danger 

 of outside contamination; the peculiar shape and structure of 

 the abdomen in these insects being especially adapted to this 

 operation. 



For removing the caeca aseptically it was found, after a number 

 of methods had been tested, that the following simple procedure 

 was really the most satisfactory. The insect is first lightly 

 chloroformed to prevent struggling, the wings are clipped off near 

 the base and the whole body moistened with alcohol to remove the 

 film of air and allow the penetration of the bichloride solution 



