Among the most suggestive results obtained through recent work in experimental embryology are those of Prof. Jacques Loeb, of the University of Chicago, on the chemical fertilization of the eggs of sea-urchins without participation of the male element. There has for some time been reason to suspect that cell-division, both in tissue cells and in the egg, is incited by chemical stimulus; and several observers before Loeb had shown that when unfertilized sea-urchin eggs are treated by the addition to the sea-water of various substances, such as strychnine or chlorides of sodium or magnesium, they may undergo some of the preliminary changes of development and may even segment. Loeb was able to induce complete and normal development by first bringing the eggs for about two hours into a mixture of sea-water and a weak solution of magnesium chloride, and then transferring them to normal sea-water. Eggs thus treated segmented and underwent a development which, though somewhat slower than usual, was otherwise normal and produced perfect larvæ. This effect can not properly be called fertilization in the ordinary sense of the word, but is rather to be regarded as artificially induced parthenogenesis. It points unmistakably, however, to the possibility, or rather probability, that in normal fertilization the spermatozoon incites the egg to development by bringing to it certain definite chemical substances; and Loeb gives reasons for the view that these substances are probably in the form of ions, concluding that these and not the nucleins are essential to the process of fertilization. A highly suggestive new field for work is opened by these experiments. * * * * *