The Poison Glands of the Larva of the Brown-Tail Moth (Euproctis chrysorrhoea Linn.)

It is well known that certain lepidopterous larvae possess urticating hairs which are the cause of a more or less severe and painful irritation when they come in contact with the human skin. In this country, the one which has attracted the most general attention on this account is the larva of the imported brown-tail moth, Euproctis chrysorrhoea. A great many cases of poisoning have been attributed to this species, and one death has been reported as the result of severe internal poisoning caused by inhaling the hairs. There has been much discussion among scientists as to whether the effect of these hairs is purely mechanical or whether they are actually poisonous, but on the other hand, singularly little definite study has been made of the morphology of the hairs and their underlying structures. It was for this reason that the subject of this paper was suggested by Dr. W. A. Riley and to him the writer is greatly indebted for much kindly criticism and many helpful suggestions. In 1894 Packard described the poisonous spines of Lagoa crispata, stating that the spines themselves were secreted by certain large trichogen cells lying under the rest of the hypodermis and connected with the spines through pore canals in the cuticle. In addition to these cells there were other smaller ones lying in different places above and below the hypodermis, and even in the pore canal itself, which he called "poison nuclei," and which he claims secrete the poison. Ingenitsky (1897) studied several different forms, especially Ochneria monacha Linn., and he clearly demonstrated that there are two cells connected with each hair and that the smaller of the two is the trichogen cell, which, after secreting the hair, decreases in size, and that the large cell is the actively secreting poison gland. Aside from the fact that Ingenitsky carefully traced the development of the two cells through all stages of the larva, this view would seem to be the reasonable one, because one would naturally expect to find that the actively secreting cell was larger than one that had already stopped its action. This latter is the same view as that expressed by Holmgren (1895). He also found that the poison hairs were connected with two cells, one somewhat larger than the other, one of which secreted the hair and the other the poison.