BIOLOGY OF LIMNERTUM VALIDUM. 77 



constitutes adaptation? We beji'in here to sink deep into the qnag- 

 mire of specuhition and doubt. We may say that tlie parasitic larva 

 is so simihir to the host in its effluvia or physical being, that its 

 presence is not felt or resented, and that it bears much the same rela- 

 tion to the host that the fetus within the uterus does to the mamma- 

 lian mother; or we may conclude that it secretes substances into the 

 blood which paralyze the protective reactions of the host. We are 

 more inclined to accept the latter view, for Ave have observed several 

 phenomena in the course of other dissections which are difficult to 

 explain except by a secretion hypothesis. 



In dissecting various parasitized insects we have often noticed 

 pathological changes in the body tissues, and especially that the 

 flaky fat bodies are often converted into a number of comparatively 

 gigantic, globular cells which are unattached and float freely about 

 in the blood of the insect. In dissecting brown-tail moth caterpillars 

 imported from Europe we have seen small first-stage larva? of 

 Meteorus exert a strange and fatal influence over the larvse of Zygo- 

 hothna nidicola Fallen, when occurring together in the same host. 

 The larvae of Meteorus live free in the body cavity of the host at the 

 extreme posterior end of the body on the dorsal side, whereas the 

 maggot of Zygobotlina is normally found encysted in the wall of the 

 crop or oesophagus. In the few cases in Avhich both were found in 

 the same caterpillar, the maggot of Zijgohothna had left its cyst in 

 the crop, and was either wandering about in the body cavity of the 

 host or had already died. How can Ave explain this strange and 

 untimely reaction of the maggot, unless we consider that it had been 

 stimulated to activity by some unusual substance in the blood tissues 

 of the host, either secreted by the larva? of Meteorus^ or by the host 

 itself in reaction thereto? 



FURTHER EXPERIMENTS WITH EUPROCTIS CIIRA'SORRHCEA. 



A third experiment was started on February 15 Avith about 100 

 brown-tail moth caterpillars that had been feeding for 20 days and 

 were consequently about 10 mm. long. These caterpillars Avere 

 placed in a small tray, and 15 females of Limnerium Avere confined 

 with them between the 15th and 27th of February, fresh females 

 being added as the first ones died. 



Dissection of living caterpillars was undertaken on the 4th of 

 March and continued on the 11th. Thirty-four caterpillars in all 

 were dissected and 15 Avere found to be parasitized by Lhnnenwn. 

 Not more than 2 larva? or eggs were found, on an average, in a single 

 caterpillar, and the larvae were in most cases dead. Oi^^y one lar\^a, 

 in fact, had obtained any size, and it Avas only alxmt six times as 

 large as the newly hatched larva\ Although incrusted Avith a capsule 

 of amcebocytes it may have been still alive, but could not liaA'e surviA^ed 



