villi in the intestine, in its undistended state, nearly fill up the whole calibre; they are arranged in longitudinal rows, and when examined in a leech newly killed, with their epithelial investment entire, they form a beautiful subject for microscopical investigation.
Food.—If the alimentary canal of the horse-leech (fig. l, p. 17) be now compared with that of the medicinal species (fig. m), one cannot fail to observe many striking differences between the two; the stomach in the one being nearly a simple cylindrical tube, whilst in the other it is provided with large lateral sacs or pouches. The cœca, which, in the horse-leech, are so small as to be very easily overlooked, are in the medicinal one of so large a size as to occupy nearly the inferior fourth of the body; the intestine, too, which in the former animal is equal in diameter to the stomach itself, in the latter is so small as to have led many anatomists to deny its existence. These facts, combined with others which have been already alluded to when describing the very great differences in their dental apparatus, cannot fail to prove that the two species must differ as widely in their habits and the quality of their food. It is still maintained by some authors, and the name—horse-leech—which has been given to this species, would tend to support the opinion, that it lived by sanguisuction, and poisonous effects have been attributed to its bite; but many persons, whose veracity cannot be doubted, after repeated trials have failed to make this species adhere to the human skin. Any one who will keep a few horse-leeches in a bottle, and supply them with worms or the larvae of insects, will soon be convinced of the voracity of their appetite, for they will devour the medicinal leech, and even individuals of their own species. All this is perfectly intelligible, and what an examination of the arrangement of their digestive apparatus, would lead us to suspect was the nature of their food. The medicinal leech, on the contrary, provided as it is with upwards of two hundred cutting teeth, and with a capacious sacculated stomach, with a small œsophagus and still smaller intestine, is eminently qualified for subsisting on liquid food; and as it is a well ascertained fact, that when once they have gorged themselves, the blood will remain for a very long time in their stomach, to all appearance in an unaltered state, it would follow either that their digestive powers must be exceedingly slow, or that the food which they take in with such avidity cannot afford them much nourishment. Is it not more probable, as Professor Kymer Jones has suggested,[1] that the complicated stomach and inferior den-
- ↑ 'General Outline of the Animal Kingdom,' p. 193.
