GASTRIC CMCA OF THE HETEROPTERA. 121 



organism that had appeared in the cultures from the first seven 

 insects tested. 



This series of experiments appeared to show very conclusively 

 that we had at last succeeded in growing the csecal bacteria in 

 pure culture, provided of course that foreign bacteria were ex- 

 cluded as completely from the alimentary canal of Anasa as 

 they had been shown to be in the Pentatomidae. Subcultures 

 were not started from these tubes for seven or eight days and 

 upon examining them again at the end of this time, a number were 

 found to contain organisms so different from the caeca! bacteria 

 that there was apparently no escape from the conclusion that 

 the cultures had become in some way contaminated. When 

 examined upon the first appearance of growth, nothing was found 

 but the short uniform bacillus, which was as much like the 

 bacteria direct from the caeca as could be imagined; but at a 

 later examination two apparently distinct contaminating forms 

 were discovered. One of these apparent invaders was a fairly 

 uniform rod-shaped bacillus 4-8 microns long by I micron 

 wide, so much larger and longer than the typical csecal organism 

 that the two could be distinguished at a glance. The other was 

 a perfectly spherical form, 0.5-0.7 of a micron in diameter, which 

 occurred commonly in extremely long chains of a hundred or 

 more individuals. 



Contamination from some source had apparently taken place 

 in a number of tubes, and it was therefore decided to discard 

 the whole series rather than attempt to make a detailed study 

 of the different forms that might be isolated from the cultures in 

 an attempt to connect some one of these with the species 

 from the glands an undertaking evidently little short of 

 hopeless. Another cause of uncertainty here was the fact that 

 the caecal bacteria from the Pentatomidae would not develop on 

 ordinary media; and as there was no reason whatever for assum- 

 ing that the forms from the Coreidae would behave any differently, 

 there was clearly a possibility that the growth that had appeared 

 in all the tubes was really contamination and that the true caecal 

 bacillus was not represented here at all. 



If the property of totally excluding all other bacteria from the 

 alimentary canal did not hold for the caecal bacteria of the 



