Page:Popular Science Monthly Volume 17.djvu/497

Rh small part of the northern coast of Africa. In some of these relatively confined regions it has been exterminated. The demand for it has become very great; France and Germany, for example, use about thirty million, and the exportation from Hamburg alone has been thirty million in a year. It is not surprising that so important a demand has raised the price of leeches till they have become a very profitable article of trade.

The successful stocking of a pond with leeches is a work requiring considerable care; the animal has many enemies, against which it must be protected, and will not thrive except under specially favorable conditions. The mother-leeches, when planted in the pond, lay their cocoons (which contain the eggs) as in nature, and the young brood is hatched out at the proper time; but this brood, besides protection, requires its natural food, sickens if it does not find it, and can not be fed artificially. The young worms will not thrive in artificial ponds; neither can they be transplanted from other countries and left to themselves without having first undergone a process of acclimatization. The most suitable ponds for acclimatizing leeches should be dug in bog-lands to a depth of about six feet, and should have from about six to ten inches of bog-soil on the bottom. The pond should contain about three feet of water, and should be provided with an inflow of fresh water and be surrounded with a wall two or three feet high. If the leeches are put in the pond in May or June, they will deposit their cocoons toward September in funnel-shaped holes in the peaty bottom; in the course of a few days some ten or fifteen young

 Fig. 3.—8. The jaw, with its saw like tooth-plates. 9. The head, with its three-parted month opening. 10. The upper side of the head, with ten eyes. 11. Section of a cocoon with its eggs.

leeches will come out from the cocoon, and will attach themselves to the old one to suck from it till they are large enough to seek food for themselves. For food, the pond should be furnished with calamus and other reed-like plants; and duck-weed, little fishes, snails and frogs should be put into it. Toward the latter part of the fall the animals