MICROSYMBIOSIS 81 



the symbionts form a closely packed group at one pole 

 of the egg. This process reminds one somewhat of the 

 nebenkern formation, as described by Bowen and others. 

 The nucleus of the ovum develops a pecuhar activity 

 during the early stages of the symbiont migration into the 

 egg. Parts of the nucleus appear to be thrown off into the 

 cytoplasm so that the ovum appears to become multinu- 

 cleate. Buchner believes that these bodies originate from 

 the nucleolus. 



Mycetocytes are also to be found in the wood-boring 

 insects. Buchner investigated some of these forms, and 

 gives a comprehensive description of their relationships 

 and the mode of transmission of the symbionts. In Lito- 

 drepa panicea there are peculiar rounded outpocketings of 

 the foregut, which are composed of mycetocytes with a 

 few compressed entodermal cells. These mycetocytes con- 

 tain symbiotic yeast cells, which are oval in outline and 

 usually contain a large vacuole. Escherich ('00) was 

 able to cultivate them in artificial culture media. The 

 eggs of the host do not contain the yeast symbionts, but 

 Buchner found them clinging to the surface of the egg 

 capsule. 



Buchner discusses the physiological significance of the 

 symbiotic yeasts in these animals. A primitive type of 

 gland organ is indicated by the outpocketings of the gut 

 tube. The digesting food mass or chyme lodges in these 

 pockets. He beUeves that the yeast cells of the myceto- 

 cytes produce enzymes which are secreted into the gut 

 lumen, and act as ferments digesting the food for the 

 insect. Such an interpretation, he mentions, is strength- 

 ened by a similar utihzation of microorganisms in the 

 digestion of cellulose in the herbivora. In these higher ani- 

 mals, the cellulose-digesting bacteria are not intracellular 

 symbionts. They are free in the lumen of the gut tube. 



It is important to note that a large number of insect 



