An Interesting Experiment.

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noting the strange effects occasioned in the mimosæ, as they drooped their sensitive petioles when disturbed. From the forest he returned to the shores of Botofogo Bay, where he devoted himself to a study of the invertebrate animals which abounded there. The Planarian worms were a constant source of interest, specimens found near here possessing a singular tenacity to life even when the body appeared dead or lifeless, the mouth parts protruding as he touched them with his forceps, showing a high state of irritation and vitality. Darwin discovered twelve species of these interesting creatures, which he fully describes in the "Annals of Natural History." One of his experiments was to cut a planarian in two parts and devote a certain amount of time to an examination of the several members. For nearly a month he watched a marvellous transformation, namely, the formation of two separate individuals out of the single worm.

The forest in which these worms were found abounded in game, and with an old priest and a native Darwin often wandered far from the ocean. Here he first witnessed the skill with which the natives employed the knife to cut vines and creeping plants. So clever had they become that it was used as the American Indians do the tomahawk, the blade being thrown a long distance with unerring skill.

Ring-tailed or prehensile monkeys were common, and two of the bearded variety occasioned them no little trouble to capture. Though shot dead, they still clung to the limbs of a lofty tree, and the latter had to be cut down to obtain them—an arduous and

laborious operation. The forest afforded constant opportunities for observing the wonders of phosphorescent insects, the brilliant fire-fly (Lampyris occidentalis) illumining the darkest recesses with its light. Darwin's investigations with these insects showed that the light was most intense when they were irritated; where the skin was injured the light was bright, while other portions gave no evidence of phosphorescence. Decapitating one he found that the light was still uninterrupted though not as brilliant, and in a specimen which he killed the strange light gleamed for an entire day.

He collected the various forms of these insects, the larvæ and adults, and made a series of experiments that have ever been of value to those who have made them a study. The larvæ he kept alive by feeding them upon raw meat, and while watching them, he learned that they used their tails as sucking organs, and that the latter contained saliva glands which were employed in a singular manner. Thus when the larva felt the pangs of hunger, it reached its tail over and deposited upon its mouth, or the food it was preparing to eat, a drop of saliva.

The elater, or Pyrophorus luminosus, was the most conspicuous luminous insect here, abounding in vast numbers and dashing through the gloomy recesses of the forest, often followed by an apparent blaze of light.

Darwin discovered during this expedition the true explanation of the leaping powers of the elater, finding that it was due to the elasticity of the spine, which threw the insect whirling into the air like a veritable spring.

Rare Collection of Insects.

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That these woods and their immediate surroundings impressed our young hero deeply, we can readily see, as he frequently refers to the beauties and wealth of the tropical foliage, and in one instance he compares the effect to the "gayest scenery of the operahouse or the great theatres."

While in Brazil, Darwin formed the finest collection of insects ever made in this country, and remembering his youthful fondness for beetle collecting, his pleasure and enthusiasm can be appreci ated. In his notes on this work, we see evidences of the theories that he formulated in later life. He was impressed with the fact that the large butterflies seemed highly coloured to conform with the gorgeous foliage and flowers of their home.

The beautiful Papilio feronia attracted his especial attention, and he made a careful study of its peculiarities, which might well be an example to young naturalists. He noticed that it invariably alighted with its head downward, with wings extended in a horizontal plane, instead of being folded vertically. When it moved, instead of edging off it ran, using its legs nimbly for the purpose, surprising the young naturalist with its agility.

While watching this interesting creature, Darwin discovered that it made a noise, and thus was the first to listen, if not to the voice of the butterfly, to a sound that is used for a similar purpose. He noticed the noise when two butterflies were chasing each other, a slight resonant clicking coming to his ear, distinctly audible twenty yards away. He describes it as resembling a " toothed wheel passing