114 HUGH GLASGOW. 



case, and he finally decided that infection normally took place 

 in the following manner: When the fly deposits its egg in the 

 fruit of the olive, a quantity of the bacteria from the special 

 structures in the base of the ovipositor are also introduced and 

 infection only takes place when the young larva, upon hatching, 

 swallows some of the surrounding bacteria. Petri also isolated 

 a chromogenic organism from the soil of olive orchards and from 

 various parts of the olive tree which he regards as identical with 

 that from the intestine of Dacus, and he seems to think that the 

 insect originally developed its infection from this free, saprophytic 

 form. 



The organism isolated so uniformly from the eggs and caeca 

 of Anasa tristis clearly belongs in the large group of fluorescent 

 bacteria that are so common in water and in soil generally. A 

 number of strains of these saprophytic fluorescent organisms 

 have been isolated and studied from the soil about squash vines 

 and from the squashes themselves; and they clearly belong in 

 the same group with the caecal bacillus of Anasa tristis, although 

 certainly none of them are identical with it. 



CULTIVATION OF THE C^CAL BACTERIA. 



In undertaking a study of the physiological relation existing 

 between the Heteroptera and their caecal bacteria, it was very 

 evident that the whole question hinged on the cultivation of 

 these organisms, and that little or nothing could be expected 

 from such a study until pure cultures were obtained. The fact 

 that these were really normal bacteria and occurred in every 

 individual possessing the caeca, in itself presented a very serious 

 obstacle to the culture work, since this very fact apparently 

 excluded all possibility of confirming, by direct infection experi- 

 ments, any cultures that might be obtained from the caeca. An 

 attempt was made, as has already been mentioned, to rear sterile 

 individuals from the egg in aseptic cages, in order to secure 

 material free from the caecal bacteria for these infection experi- 

 ments; but since the bacteria were found to pass normally 

 through the egg, these rearing experiments were unsuccessful; 

 and this apparently left no alternative but to select for the culture 

 work only those insects in which the bacteria were so character- 



