112 HUGH GLASGOW. 



outside source is required. While the occurrence of a similar 

 relation in the Heteroptera is by no means certain, there are a 

 number of facts pointed to both by direct observation and by 

 analogy, that would seem to favor this view rather than the 

 theory that the bacteria are confined strictly to their insect hosts 

 and are transmitted indefinitely from generation to generation 

 through the egg. 



One reason for the first view is that in certain of these insects, 

 as in Murgantia and in many other pentatomids, the bacteria 

 really appear to be existing under marked difficulties of some sort, 

 as indicated by the proportion of involution forms and the 

 constancy with which they appear in the caeca of these insects, 

 and also by the fact that the vast majority, at least, even in such 

 forms as the squash bug, are apparently unable to develop any 

 longer or artificial media. In the case of this particular insect, 

 while growth was uniformly secured from the caeca where liquid 

 media was used, it soon became evident, when plate cultures 

 were made direct from these organs, that but a minute fraction 

 of the bacteria actually present were able to develop on artificial 

 media, the vast majority evidently being either dead or modified 

 in such a way by their existence in the caeca that they were wholly 

 unable to develop outside the host insect. Frequently when only 

 a very short section of the caeca was removed for inoculation, 

 especially where plate cultures were made, no growth whatever 

 developed, although there were certainly thousands of bacterial 

 cells introduced. 



Another case that may throw some light of analogy on this 

 question is that of the w r ell-known symbiotic relation between 

 certain green turbellarians and their associated algee (Keeble, 

 '07). Numerous attempts have been made to cultivate these 

 algse on artificial media, but uniformly without success. This 

 w r as sometimes explained on the theory that these two organisms 

 had been associated in this relation for so long that the alga had 

 completely lost its ability to develop in the free state, and was 

 now totally dependent on the animal, as is often the case in 

 many of the more highly specialized parasites. This is certainly 

 a very reasonable view but it has recently been discovered that 

 the zoochlorellae, although exerting a profound influence on the 



