GASTRIC C/ECA OF THE HETEROPTERA. I2Q 



the squash bug, they certainly all belong to the same group and 

 the differences noted were no greater than those observed in 

 different strains from the squash bug itself. 



It was thought at one time the bacteria isolated from the 

 caeca of these insects might readily be identified as some already 

 described species known to occur free in nature, but the classifica- 

 tion of this group was found to be in such a chaotic state that this 

 idea was abandoned ; and for the same very good reason it was 

 thought that little would be gained by an attempt to describe 

 them as new. 



Some idea of the striking morphological differences in the 

 bacteria from different host species can be gained from the follow- 

 ing brief notes on a few of the more characteristic types as they 

 occur in the caeca. No attempt will be made in this article to 

 mention all of the many different morphological types of bacteria 

 that have been observed and studied in the different host species 

 dissected, the present object being merely to give examples of a 

 few of the extreme cases that are met with. For this purpose 

 the caecal organisms from Anasa tristis, BHssus leucopterus, 

 Euschistus servus, Peribalits limbolarius, and Murgantia histrionica 

 should serve very well, as in this series we get the two extreme 

 types in Anasa and Murgantia, the others representii g inter- 

 mediate forms. 



In the first two host species the normal bacteria are much 

 alike in appearance, both being very short rods which average 

 something like one micron by 0.7, those from Anasa tristis, 

 however, being usually slightly smaller and rather more slender 

 than those from the chinch bug (Plate VIII., Figs. 21 and 23). 

 In both of these insects the bacteria are quite uniform in appear- 

 ance, varying no more in size and form from the typical cells 

 than might well be expected. They occur very regularly in short 

 chains of two, occasionally of four and very rarely of six or more 

 cells, and do not show the slightest indication of motility as they 

 come from the caeca. They take the common stains readily and 

 on the whole have the appearance of ordinary bacteria with 

 nothing especially striking to characterize them. 



From Euschistus servus (Plate VIII., Fig. 24) the bacteria are 

 decidedly longer than in the insects just mentioned, although 



