BIOLOGICAL STUDIES ON INTRACELLULAR BACTERIA. 137 



served, but since the fat body surrounds the ovarioles, this is 

 highly probable. 



In Pcriplaneta bacteriocytes have been found in the oviduct. 

 No bacteria have been noticed at the periphery of young oocytes, 

 but on observing large ones a number can be seen on the surface 

 that have wandered out of the bacteriocytes, and must have made 

 their way out through the follicular membrane. As the egg 

 grows the bacteria become much more plentiful on the surface 

 forming a closed layer around the entire egg. Soon the micro- 

 organisms become more concentrated at both poles and many are 

 seen to lie perpendicular to the egg. In freshly laid eggs the bac- 

 teria are found within under the vitelline membrane, so they 

 must have left the follicle, but the exact method has not been 

 traced. 



In Blattids generally, the later development takes place as fol- 

 lows : The organisms are concentrated in the middle of the yolk. 

 The vitellophags also become infected. When the germ band 

 grows around the yolk the bacteria get into the embryonic intes- 

 tinal lumen. After a time they leave the lumen, wander through 

 the intestinal epithelium and get into certain fat cells which they 

 modify as previously shown. They take possession of the adipo- 

 cytes and render them functionless as fat cells. 



While the morphological details are not complete, they are 

 very interesting. I found very similar conditions in the two 

 species with which I worked, namely, Periplaneta anicricana and 

 Parcoblatta virginica. 



One of the most striking things in connection with this work 

 is the definite wanderings of the microorganisms. They are 

 motile forms in the insects studied by me, but that would not 

 account for the prescribed course which they follow. I believe 

 one must postulate a chemotropic response between the bacteria 

 and certain host tissues in order to account for such behavior. 



2. THE MORPHOLOGICAL, CULTURAL AND BIOCHEMICAL CHAR- 

 ACTERS OF THE ORGANISMS CULTIVATED FROM PARCOBLATTA 

 VIRGINICA AND PERIPLANETA AMERICANA. 



By dissecting cockroaches that portion of the fat body in which 

 the bacteriocvtes are embedded can be easilv removed. It is 



