Page:Popular Science Monthly Volume 13.djvu/563

Rh "fine lady" wear in the future if the prince of precious stones should follow the example of those standing closest to its throne, and allow itself to be reproduced for a few shillings?



ONTRARY to the opinion of Sellius, who regarded the teredos as hermaphrodites, Quatrefages has taught us that they are of both sexes and that the ratio of males to females is about one to twenty. The females are oviparous. The eggs are expelled by the branchial siphon: Quatrefages found them in that siphon and in the branchial canal itself. The mode of fecundation is, however, unknown; it is supposed that, in that act, two different teredos project their siphons and bring them in contact.

As regards the metamorphoses which the eggs undergo, either in the branchial tubes or in the water, nothing has been added to what was made known through the researches of Quatrefages in 1849. That naturalist has taught us that the eggs pass through the series of modifications, from the starting-point, which one meets with in the examination of all animals—i. e., the formation of the germinative area and of the vesicle of Purkinje, the disappearance of this and the breaking up of the vitellus. The eggs undergo their development in the branchial cavity of the mother; the embryos resemble very small, rounded animalcula of vesicular form, and are provided with vibratile cilia, by the aid of which they have regular movements, and probably are expelled from the branchial cavity into the siphon. In a third phase of development the bivalve shell is formed, the foot appears on the outside, the vibratile cilia form a sort of crown, and the embryo thus possesses the faculty of locomotion as well by creeping as by swimming. The development of the eggs takes place from time to time, and especially in the month of June, although even as late as the 29th of July Harting found eggs in all the teredos which he opened. The development of the eggs progresses very rapidly; in four days they pass out of the embryonic state, fully equipped for living in wood. Toward the end of June, Kater observed them in large numbers on the surface of wood, and by the 15th of July he found them in the interior in the form of perfectly-developed teredos. Even in the month of December, but no later, he saw young teredos enter into pieces of wood placed by