144 HUGH GLASGOW. 



in the bag-like salivary reservoirs instead of being excluded 

 entirely as was apparently the case in most other Heteroptera in 

 which the caeca are present. 



As a result of the apparent failure in the culture work with 

 Murgantia and the other Pentatomidse followed by the successful 

 cultivation of the caecal bacteria from Anasa tristis, it became 

 evident that at least one perfectly clear-cut function possessed 

 by these organisms, whether of profound importance to the host 

 insect or not, w r as the antagonism which they certainly show 

 towards other bacteria and protozoan parasites which would 

 normally be expected to occur in the intestine of such insects. 



In the culture work on the Pentatomidse it was found that 

 the entire caecal system of one of these insects could be removed 

 and dropped directly into a tube of bouillon or other media, 

 where it would remain for a month or more without a trace of 

 growth developing. This was not an occasional occurrence, but 

 was invariably the result secured where the Pentatomidae were 

 used and demonstrated conclusively that the caecal bacteria are 

 not only antagonistic to the ordinary saprophytic and para- 

 sitic bacteria, but prevent their development entirely, and appar- 

 ently kill them when they invade the alimentary canal of these 

 insects. 



In the somewhat similar association described by Petri for the 

 larva of Dacus olece the bacillus concerned was found to secrete 

 an active lipolytic enzyme which presumably assisted the insect 

 in digesting its oily food, but unfortunately Petri apparently did 

 not consider the possible antagonism of these caecal bacteria of the 

 fly toward the forms which commonly invade the alimentary 

 canal of such insects; and it is consequently impossible to say 

 whether the caecal bacteria of the little fly resemble those of the 

 Heteroptera in this regard or not. 



In regard to a digestive function for the caecal bacteria of the 

 Heteroptera, it can only be said that in cultures these bacteria 

 apparently secrete no enzyme that could be of any very evident 

 assistance in the digestive processes of the insect, and this agrees 

 perfectly with the peculiar localization of these organisms at the 

 extreme posterior end of the digestive portion of the gut, which 

 in itself would render the probability of their assuming an impor- 



