76 RESULTS FROM GIPSY MOTH PARASITE LABORATORY. 



larva^ of Limnenum arc free from the slightest trace of aiiKX'bocytic 

 attack Avhen occurring in their natural host. 



Other phases of this so-called "phagocytosis" have been studied 

 by several European investigators, especially by Cuenot (IS'JC)), 

 Janet (190G, 1907), and Pantel (1910). The latter author has given 

 a summary of those cases of amccbocytosis that were known to him 

 in his excellent '•'■ Rccherchcs sur Zcv Dipteres a Larves Entomohies?'' 

 He concludes that this defensive reaction of the host is aroused not 

 only by bacterial infection but also by sick or dead parasitic larvae 

 and by molt skins, and states that free and healthy larvoe are regu- 

 larly exempt. 



The only cases of sick larvae that Pantel seems to have observed 

 are larva? of Tachinidse that have fallen accidentally from their 

 breathing holes, generally during the molting of the host. Such 

 larvffi do not affix themselves anew, but wander about in the body 

 cavity of the host until overcome by suffocation. Pantel further ob- 

 serves that the anal sheaths of such larvse begin to turn brown and 

 become inclosed by a great number of ainoebocytes, which finally 

 almost completely cover the larva. 



In the case of dead larvae which have perished in the struggle for 

 the possession of the host, Pantel observes that their bodies only 

 exceptionally become incapsulated by amoebocytes. The molt skins, 

 on the other hand, he furthermore states, are attacked, not always, 

 but most frequently by amoebocytes. 



The similar action of amrebocytes in breaking down the wing mus- 

 cles of queen ants has been described by Janet (1906, 1907). The 

 muscles are not devoured in small fragments by phagocytes, but are 

 disintegrated gradually and absorbed by amoebocytes, which creep in 

 among the fibrillar in large numbers. 



We have seemingly in this amcebocytic reaction a manifestation of 

 the protective faculty of the host in guarding against the attack of 

 entoparasites. As shown by Pantel (1910) and confirmed by our 

 own observations of various species of parasitic Diptera and Ilymen- 

 optera, normal or adapted parasitic larvae, when healthy, rarely if 

 ever arouse this defensive reaction, or, in other possibly more correct 

 words, they are able to repel the amoebocytes by some curious adapta- 

 tion. Unadapted parasites, on the contrary, being unable to repel the 

 amoebocytes, may regularly succumb to their agenc}^ The instinct of 

 parasites under ordinary conditions well fits them for choosing their 

 accustomed hosts, but in the millions of instances where this instinct 

 co'^nes into play, an q^^ may be placed occasionally in an unsuitable 

 host. In such cases the resulting larva seems to be doomed to a lin- 

 gering death, and its tissues are absorbed by the amtebocytes with 

 no ultimate detriment to the host. 



ADAPTATION OF PARASITi: TO HOST. 



The jjlienomenon of amoebocytosis. on the other hand, brings up the 

 question. Why do not all parasites suffer the same fate, and what 



