10 



development in the seed pieces the maggots leave this 

 abode, enter the soil, and pupate. In this manner the 

 "bacteria survive the winter in the digestive tract of the 

 puparia. Besides Erwinia carotovora , other "bacteria 

 regularly pass uninjured through the intestinal tract of- 

 "both larvae and flies and over -winter in the puparia and 

 emerge with the adult fly. The most common of these are: 

 Pseudomonas fluoresence and Ps. nonliquefaciens . Leach 

 (1933) found the "bacteria survive in the puparium in three 

 different locations : in the cast-out linings of the hind- 

 intestine, and in the lumen of the mid- intestine of the 

 pupa. The "bacteria found surviving in the fore- and hind- 

 intestines may "be of several varieties since they are the 

 ones that happen to be in these organs at the time of 

 pupation. In the mid- intestine, on the other hand, the 

 "bacteria appear to be of one species resembling, "but not 

 identical to, Pseudomonas fluoresence . These "bacteria 

 "become reduced to relatively small numbers during meta- 

 morphic histolysis "but just "before the fly emerges from 

 the puparium they appear to increase rap idly . According 

 to Leach, there appears to "be a selective action on the 

 "bacteria surviving in the mid-intestine that is not 

 operative on those surviving in the cast-off linings of 

 the fore- and hind-intestines. 



Eelationships similar to those just described exist 

 "between Erwinia caratovora and the cabbage maggot, 

 r iylemyia brassicae . Phytomonas savastonoi , the cause of 

 olive knot, is also known to survive in the puparium of 

 the olive fly, Dae us oleae (Petri, 1910). 



Transmission of Bacteria from Generation to Generation , 

 Along with the discussion of the fate of bacteria during 

 metamorphosis should be mentioned the phenomenon of trans- 

 mission of bacteria from one generation to the next» Many 

 instances of this process are known to occur with intra- 

 cellular microorganisms. 



An outstanding example of the perpetuation of extra- 

 cellular bacteria through successive generation has been 

 described by Petri (1909, 1910) in the case of Phytomonas 

 savastonoi , the cause of olive knot, and the non-patho- 

 genic bacterium, Ascobacterium luteum in the olive fly, 

 Dacus oleae . These bacteria occur in the intestinal tract 

 during all stages of the insect's development. 



If one were to make a longitudinal section of the 

 ovipositor of the olive fly, he would observe that the 



