IIO HUGH GLASGOW. 



At this time no more eggs of the squash bug were available, 

 and the cultures from them had all been discarded as of no sig- 

 nificance; but the following season, when the matter was again 

 investigated in the light of these new facts, it was found that the 

 cultures that developed so regularly from the eggs of this insect 

 were identical with those that were also secured from the caeca, 

 and that instead of containing a number of contaminating 

 organisms, the growth really consisted of a pure culture of the 

 caecal bacillus. The reason for believing, at first, that the cul- 

 tures from the eggs represented more than one organism and the 

 fact that no growth was secured from the eggs of Murgantia are 

 discussed in connection with the regular culture work; and it is 

 enough to say here that when ordinary care was taken in the 

 disinfection of the eggs of Anasa tristis, the resulting growth was 

 invariably a pure culture of the ca?cal bacillus. 



Ic was also established for a number of other species, including 

 the lygaeid, Blissus leucopterus, that the bacteria are present in 

 the caeca of the nymph immediately after hatching, and conse- 

 quently, at a time when all outside contamination could be 

 excluded; but it was considered a piece of unnecessary routine 

 to attempt to carry the examination back into the embryo of 

 these forms as had been done in the case of Anasa tristis and 

 Murgantia histrionica. 



The exact manner in which the caecal association developed 

 in these insects can, of course, only be surmised. It is possible 

 that the present normal bacteria were formerly pathogenic for 

 the host, and that the caeca, as they now exist, originally developed 

 from true pathological structures formed as a result of the inva- 

 sion of the tissues by these organisms; or the bacteria may 

 originally have been merely saprophytic forms, peculiar to this 

 section of the alimentary canal, which gradually became adjusted 

 to an existence in the caeca. 



One factor that might be regarded as supporting the first 

 view is the fact that the bacteria are, to a certain extent, intra- 

 cellular; and it is easy to imagine how these otganisms, originally 

 attacking certain of the epithelial cells of the gut, might have 

 stimulated the formation of pathological caeca, which, being 

 incidentally of some use to the host, were preserved and even 



