ARTIFICIAL PARTHENOGENESIS. Experiments by Herbst, E. Hertwig, T. H. Morgan, and espe cially by Loeb, show that the unfertilized eggs of the sea-urchin may be so stimulated by chemi cal solutions as to undergo the earlier phases of development. Herbst experimented with potas sium chloride and lithium chloride, but found that while the lame developed, they were mon strous and finally perished. Hertwig and also :Morgan showed that if unfertilized eggs be treated by weak solutions of sodium chloride, magnesium chloride, or strychnine, they exhibit some of the preparatory changes of yolk-division, and might actually divide, though without pro ducing an embryo. Loch finally succeeded in rearing large numbers of perfect larvm • from eggs which, without fertilization, are first treated with a weak solution of magnesium chloride, and then transferred to normal sea-water. It thus appears that experiments carried out under rigidly controlled conditions show that the egg, without union with a sperm-cell, is capable of complete development. In commenting on these
discoveries E. B. Wilson (International Monthly, July, 1900) remarks that even in normal fer tilization we must regard the stimulus to devel opment as being given by a specific substance or substances carried by the spermatozoon. The ex periments lead us to suppose that the chemical salts used "are individually poisonous to the egg, but are normally so balanced as to neu tralize one another's injurious effects and main tain the equilibrium of the egg. If this armed neutrality he disturbed, the egg responds, under going degenerative changes, and dying if the ehange be too violent, passing through an abnor mal development and giving rise to monstrous embryos if the new conditions be less unfavorable, but under appropriate stimulus being, as it were, released from bondage, and rendered free to run its normal course of development."