Vol. XX VI. March, 1914. No. j 



BIOLOGICAL BULLETIN 



THE GASTRIC C^ECA AND THE C^CAL BACTERIA 

 OF THE HETEROPTERA. 



HUGH GLASGOW. 



TABLE OF CONTENTS. 



I. Summary 101 



II. Introduction 102 



III. Constancy of the Caecal Infection 104 



IV. Origin of the Caecal Infection 106 



V. Cultivation of the Caecal Bacteria 114 



VI. Function and Phylogenetic Significance of the Caeca in the Heteroptera. 131 



VII. Functional Relation of the Bacteria to the Host Insect 141 



VIII. Importance of the "Normal" Intestinal Bacteria to the Host 146 



IX. References 153 



X. Explanation of Plates 156 



SUMMARY. 



1 . Certain of the Heteroptera are almost unique among insects 

 in the possession of well-developed caecal appendages situated 

 at the extreme posterior end of the digestive portion of the gut. 



2. The caeca are remarkable in that wherever they occur they 

 are invariably filled with bacteria. 



3. These bacteria are not only always present in the caeca of 

 normal bugs but the association is hereditary, the organisms 

 appearing early in the alimentary canal of the developing embryo. 



4. Structurally the bacteria from different hosts vary greatly, 

 ranging from minute, coccus-like bacilli measuring often less 

 than one micron, to huge, spirochsete-like forms thirty microns 

 and more in length ; but in whatever form they occur they are 

 morphologically characteristic for the particular species harboring 

 them. 



5. That these are unquestionably bacteria is sho\vn conclu- 

 sively by culture experiments checked by agglutination tests. 



6. These normal bacteria appear not only to inhibit the de- 

 velopment of foreign bacteria but to exclude them altogether, 



101 



