We have few direct observations on the nature of the food of _Leptoplana_, or the exact mode by which it is obtained. Dalyell,[18] who observed this species very carefully, noticed that it was nocturnal and fed upon a _Nereis_, becoming greatly distended and of a green colour after the meal, but pale after a long fast. Keferstein[19] noticed a specimen in the act of devouring a _Lumbriconereis_ longer than itself, and also found the radulae of _Chiton_ and Taenioglossate Molluscs in the intestine. That such an apparently weak and defenceless animal does overpower large and healthy Annelids and Mollusca, has not hitherto been definitely proved. Weak or diseased examples may be chiefly selected. The flexible _Leptoplana_ adheres firmly to its prey, and the rapid action of the salivary glands of its mobile pharynx quickly softens and disintegrates the internal parts of the victim. The food passes into the stomach (Fig. 2, _mg_), and is there digested. It is then transferred to the lateral branches of the intestine, and, after all the nutritious matters have been absorbed, the faeces are ejected with a sudden contraction of the whole body through the pharynx into the water. _Leptoplana_ probably does not live more than a year. In the spring or summer, batches of eggs are laid and fixed to algae or stones by one individual, after having been fertilised by another. Young _Leptoplana_ hatch out in two to three weeks, and lead a {11}pelagic existence till they are three or four millimetres in length. In late summer, numbers of such immature examples may be found among sea-weeds and _Corallina_ in tide pools. In the succeeding spring they develop first the male and then the female reproductive organs. [Illustration: FIG. 4.—Portion of a transverse section of _Leptoplana tremellaris_ in the hinder part of the body. × 100. _bm_, Basement (skeletal) membrane; _cil_, cilia; _d.m_, diagonal muscles; _d.v.m_, dorso-ventral muscles; _ep_, epidermis; _f.p_, food particles; _l.g_, lateral intestinal branches cut across; _l.m ext_, external, and _l.m int_, internal longitudinal muscle layers; _m.c_, glandular (mucous) cells; _md_, their ducts; _N_, longitudinal nerve; _Nu_, nuclei of the intestinal epithelium; _ov_, ovary; _ovd_, oviduct; _par_, cells of the parenchyma; _r.d_, vasa deferentia, with spermatozoa; _rm_, circular musculature; _rh_, rhabdites; _sh_, cells of the shell-gland; _te_, testes; _ve_, vasa efferentia; _y.c_, "yellow cells." (After Lang.)]