128 HUGH GLASGOW. 



It was firmly expected, when the present investigation was 

 undertaken, that the characteristic and remarkably varied 

 types of caecal organisms observed in the different Heteroptera 

 would be found to represent a large number of different species 

 and perhaps genera, and that a very careful study and descrip- 

 tion of each type, at least as they occur in the caeca, would be 

 necessary. In view of the results which have developed from 

 the culture work, however, it seems probable, almost certain in 

 fact, that all of these strikingly different forms really belong to a 

 single clearly defined group of bacteria, and that the differences 

 in structure that are so constant for the given host species are 

 due to some specific physiological peculiarity of the insect which 

 exerts a very definite influence in determining the morphology 

 of the bacterial cell. 



While all of the different strains isolated from the cxca. and 

 eggs of Anasa tristis belong to the group already mentioned, 

 they are by no means all identical in their behavior on artificial 

 media. The most striking of the differences observed was in 

 the vigor with which they developed in culture, some strains 

 showing a remarkably strong growth from the very beginning, 

 others making a comparatively very weak growth even after 

 repeated transfers, while occasionally a strain would be found 

 which, growing very feebly at first, gradually weakened for some 

 unknown reason and finally refused to grow altogether after 

 three or four transfers. 



Another thing that I have not yet been able to do is to make 

 a detailed comparison of the cultural characters of the different 

 strains isolated from the squash bug, but from the observations 

 already made there is undoubtedly considerable variation in the 

 minor cultural characters in many of these. 



Quite recently in working with other coreids than Anasa tristis, 

 cultures have been secured regularly from the caeca of Alydus 

 quinquespinosus, Aldyus conspersus, and Metapodius terminalis, 

 as well as from the eggs of the first species of Alydus, although 

 cultures attempted from the eggs of a single female of Ardrimerus 

 indecorus were uniformly negative. 



While the bacteria isolated from these three coreids show 

 certain slight differences in culture from the typical strains from 



