become a male, temporarily ceases to feed, shrinks within its old skin, develops a thin new one, and ultimately becomes a long eel-like worm (Fig. 134, 6, 7, 8), which grows into an adult male (8). In the stage represented in Fig. 134, 8, the animal still lies under the outer skin of the root, which never bursts during its development, but the mature male bores out of its larval skin and out of the root, passing into the soil, where it finds and fertilizes the female, which in the meantime has developed but remains attached to the root. The female develops in a simpler way, by the gradual distension and growth of a larva (not by a process of re-formation) and gradual development of the female sexual organs. As the larva passes from the stage of Fig. 134, 5, into that of Fig. 134, 9, and later on into the adult condition, 10, the outer skin of the rootlet is ruptured, and the female comes out from its tissues, remaining, however, attached to its outside (Fig. 134, 1). The entire development from egg to sexual adult takes four or five weeks, and there may be six or seven successive generations, the reproduction is consequently very rapid. It also obviously follows that “beet sickness” of the soil is especially prevalent in fields where there has been an excessive amount of beet culture. The disease, however, may suddenly appear in fields which have been hitherto “safe” for beet, and in many such cases it has been proved to result from manuring with artificial compost rich in refuse from affected fields. The disease frequently appears, too, in fields where beet have never been cultivated, but where cabbage has been grown for a long time. It has been shown, especially by Kühn’s investigations, that the beet eelworm can live in many plants both cultivated and wild, _e.g._ of the former, cabbage, rape, mustard, garden cress, chickling peas, mangold, oats; of the latter, charlock, spurrey, couch grass. These researches are of the greatest importance both for understanding the way in which beet sickness spreads and in combating it.