A NUTRITIONAL STUDY OF INSECTS 73 



Sulc ('10b), and as absorbers of excess food materials such as 

 sugar, according to Pierantoni ('10). 



The movements and location of the symbionts has been studied 

 by Buchner ('12) in a great work on the Blattidae. Glasgow 

 ('14) has also studied a case of symbiosis in which the microor- 

 ganism, instead of being located in a fat-body (mycetocytes) , as 

 in the cockroaches, is retained in very highly developed gastric 

 caeca of the plant bugs (Heteroptera) . The function ascribed 

 to the bacteria by Glasgow is the prevention of infection of the 

 digestive tract by other bacteria. Dissected digestive tracts on 

 bacterial media gave only pure growths of the associated micro- 

 organisms. Petri ('04, '05, '06) studied the similar case of Dacus 

 oleae, which feeds on the olive, but ascribes to the bacillus 

 alipolytic enzyme of assistance in the digestion of the food. 

 Schaudinn ('04) finds that a fungus (Entomophthorineae) is 

 transmitted through the egg of Culex and is always found in the 

 diverticulae of the oesophagus of adult Anopheles and Culex. 

 He has been able to rear the fungus in sugar solution and has 

 demonstrated that CO2 is formed in the imago from the sugars in 

 the blood which it has sucked up. It is probable that the irri- 

 tation caused by the bite of mosquitoes is largely due to enzymes 

 secreted by these fungi. 



In these cases the associated fungus may be a commensal, in 

 its relation to the host, profiting by an oversupply of some food 

 substance, as in the case of aphids, mosquitoes, etc., or may 

 be of value as a chemical agent, as in the case of Dacus oleae, 

 or may be of service in maintaining an unchanged digestive flora, 

 as in the Heteroptera, as described by Glasgow. In general, 

 however, the exact function of the microorganism to its host has 

 not been thoroughly explained. 



CONCLUSION 



I have shown by experiments that Drosophila living in fer- 

 menting fruit are dependent for their food supply on the synthetic 

 and absorptive powers of yeast cells. In a similar manner, my 

 study of the relation of Musca domestica to manure, of Desmome- 

 topa to decaying meat, and of Sciara and Tyroglyphus to decaying 



