104 HUGH GLASGOW. 



part of the work on the bacteriology of the subject, although at 

 that time the laboratory was so crowded that few men would 

 have thought of admitting me. 



CONSTANCY OF THE C,ECAL INFECTION IN HETEROPTERA. 



One of the first questions that came up in connection with the 

 work was that of the constancy of the bacterial infection of the 

 caeca whether these organs were always infected and whether 

 the infecting organism was always the same. It had been 

 established by Professor Forbes that the infection in Blissus 

 leucoptems was constant throughout the range of this insect in 

 Illinois, and all the Heteroptera in the neighborhood of Urbana, 

 in which the caeca were present, also showed the infection; but 

 to make certain that this relation was one of fundamental 

 significance and that the infection was not merely a local phe- 

 nomenon, peculiar to the Heteroptera of Urbana, or perhaps of 

 Illinois, it was planned to select some common, widely distributed 

 species and to examine specimens from as great a range as 

 possible. 



It was necessary, of course, that the species selected for a study 

 of this kind should be widely distributed as well as common and 

 easy to collect and, what was of even greater importance, that 

 the csecal bacteria should be characteristic in form, to insure that 

 the infection was not due to different species of bacteria of similar 

 form occurring in different parts of the range of the insect. 



The harlequin cabbage bug, Murgantia histrionica, was finally 

 chosen as the species most nearly fulfilling these conditions. It 

 ranges from California across the southern half of the United 

 States and thence to New England; and it is usually a very 

 common and conspicuous form wherever cabbage is grown; but 

 what made it especially suitable for this test was the large size 

 and remarkable form of its caecal bacteria (Plate VIII., Fig. 26). 

 Instead of being minute, short rods, as in Anasa tristis and 

 Blissus lencoptems, the only two other species available for the 

 test, those of Murgantia are very large, contorted, spirochaete- 

 like forms which could not possibly be mistaken for any of the 

 other varieties of caecal bacteria. 



To secure specimens, requests for living material were sent to 



