BIOLOGY OF LIMNERTUM VALIDUM. 75 



AMCEBOCYTOSIS AS A PROTECTIVE KEACTION OF THE HOST. 



The remarkable fact in the array of figures just given is the 

 disparity between the number of eggshells or cast choria found and 

 the number of larv«. The latter were large enough so that they could 

 not have been overlooked, and the only explanation is that they had 

 been killed by the host and absorbed by the blood tissues, or de- 

 stroyed, in other words, by amoebocytosis. The chitinous choria, 

 on the other hand, escaped unharmed. In the preceding experiment, 

 in one of the dead caterpillars dissected on February 15 the dead 

 larva? and some of the eggs and eggshells were found inclosed in a 

 firm, thick, homogeneous-appearing, transparent capsule of tissue. 

 The significance of this was not realized at that time, but when on 

 February 19 the same phenomenon was noticed in the dissection of 

 living caterpillars, the mystery of the missing larva? was explained, 

 for wdien the capsule was stained in methyl green and mounted in 

 glycerin, it was resolved under the high power of the microscope 

 into innumerable, densely packed, minute, roundish and spindle- 

 shaped cells. These were undoubtedly blood-tissue cells or amoebo- 

 cytes, and whereas they were not true phagocytes, yet their func- 

 tion must have been to break down and absorb the tissues of the 

 parasites, for within the capsules larva? were found in several stages 

 of dissolution. 



Later experiments with the same and other hosts, such as Mala- 

 cosoma and Noiolophus, brought to light the fact that this amoebo- 

 cytic reaction takes place regularly when the Limnerium occurs in 

 these hosts to which it seems to be unaccustomed and unadapted. 

 In most cases it was found that the parasite was able to hatch from 

 its egg, but that it perished generally soon afterwards before growing 

 to any extent. Many times the larva was found to have disappeared 

 entirely through the action of the amoebocytes, yet the story of its 

 death and dissolution was told by the encapsulated remains of the 

 much more resistant* eggshell. Whether the amwbocytes gathered 

 around and killed the living larva? and eggs or attacked only para- 

 sites that had been killed by some other factor was not certainly de- 

 termined; but the former supposition is probably correct, as un- 

 hatched eggs containing embryos in ditferent stages of dissolution 

 were found sometimes inclosed in sheaths of these cells. In one in- 

 stance, also, a larva that had grown to be about six times the size of 

 newly hatched larvse, was found entirely inclosed except for its head 

 in a characteristic sheath. This larva was probably living wlien 

 its host was killed for dissection, or at least, judging from its fresh 

 and uninjured condition, it could not have been dead for more than 

 a few hours. 



An extended series of dissections of Hyphantria cunea, on the other 

 hand, made by J. D. Tothill during the fall of 1910, showed that the 

 34176°— No. 19, Pt. V— 12 2 



