144 R - W - GLASER. 



organisms now found as harmless entities within the insects were 

 parasites producing pathologic conditions and disease. It seems 

 to me, that such structures as the mycetocytes, bacteriocytes and 

 mycetomes are a survival of previous profound pathologic 

 changes. Later acquired immunity principles became heritable 

 and the toxins and other effects came under control. The insects 

 could not fully rid themselves of the invaders on account of the 

 fact that transmission from generation to generation had estab- 

 lished itself with unerring precision. Still later, the micro- 

 organisms lost all of their harmful effects and since they secreted a 

 number of enzymes that proved serviceable to the hosts, the latter 

 were not exterminated, but were probably diverted from their 

 normal phylogenetic course. It is interesting to reflect what 

 would have happened to those insects that harbor intracellular 

 organisms if they had never been invaded by the parasites. If 

 the hosts had not been able to overcome the infection they would 

 have become extinct or at least reduced numerically to an appre- 

 ciable extent. However, the insects were able to adapt them- 

 selves to profound changes and the phylogenetic history must 

 have likewise taken another course. It is impossible to imagine 

 that such structures as the pseudovitellus, mycetocytes and myce- 

 tomes with their inhabitants could have developed without altering 

 the physiology and morphology and consequently the habits of 

 the host. 



The microorganisms may, as Buchner suggests, derive some 

 benefit from the association, but this is not clear since they prob- 

 ably derived much more benefit as true parasites or disease pro- 

 ducers. Judging from the ease with which the Blattid symbionts 

 can be cultivated on almost anything, I feel sure that had they 

 succeeded in exterminating all Blattids, they would still persist 

 today living possibly as saprophytes under much more advan- 

 tageous conditions. 



LITERATURE CITED. 

 Balbiani. 



'66 Note sur la reproduction et embryogenie des Pucerons. C. R. Acad. 

 Sc. Paris, Vol. 62. 



'75 Sur 1'embryogenie de la Puce. C. R. Acad. Sc. Paris, Vol. Si. 

 Blochmann, F. 



'87 Uber das regelmassige Vorkommen von bakterienahnlichen Gebilden in 

 den Geweben und Eiern verschiedener Insekten. Ztschr. Biol., Vol. 24 

 (N.F., Vol. 6). 



