Zoology: Development of Molgula Tubulosa

Abstract

IT is well known that the larvse of the Ascidians generally possess a form resembling, in external appearance at least, that of the tadpoles of our common Frogs, and also resembling these in the agility with which they swim about by means of their tail-like appendage. In fact, as M. Lacaze Duthiers indicates in a paper just communicated to the Academy of Sciences, this peculiarity of development has for a long time been regarded as characteristic of all the Ascidians. According to the celebrated naturalist just mentioned, Molgula tubulosa forms an exception to this general rule. Instead of exhibiting the brisk, jerking movements of the embryos of the Phallusiœ for example, the embryo of Molgula moves very slowly within its egg-capsule, its movements consisting chiefly of alterations in its general form which, however, finally effect the rupture of the capsule. Through this opening the embryo flows, like a plastic, amœboid mass, which remains quietly at the bottom of the vessel, merely changing its form slowly by amœboid movements. Soon after exclusion the embryo shows indications of zones in its body, and from the outermost of these processes are given off (for some time only five in number), which seem to fix it to surrounding objects and are analogous to the innumerable filaments of the tunic in the adult.