V. On the development of lepas fascicularis and the “archizoëa” of cirripedia

Abstract

B urmeister’s important discovery that in Lepas the larvae pass through a and a Cyprisstage was made on the same Lepas which forms the subject of this paper. B urm eister*, however, had evidently only a ball of this , some specimens of which were young in the Cypris stage, which had just settled; while others were dismissing young Naupli, which, unless great care is taken, die very soon in captivity. He thus missed the intermediate stages, which, however, were at that time much less important, as the first thing that was wanted then was to establish the general outlines of the Cirriped development. The Nauplius of this Lepas has since been seen by D arw in f , to whom H ancock showed it, “ calling his attention to a proboscidiform projection on the underside of the larva of Lepas fascicularis when just escaped from the egg.” Neither J. v. T hompson’s nor P agensteciier’s observations refer, as far as I can find out here, to Lepas fascicularis; and it seems not to have been taken up again as an object for embryological researches until C laus published his paper on the Cypris-\ike larva (pupa) of the Cirripeds and its metamorphosis into the fixed animal (Marburg, 1869), a paper of which I have unfortunately only an abstract, as given by N itsciie in his embryological report for the year 1872, and by C laus himself in his ‘ Grundziige der Zoologie,’ which, however, affords nearly all the information necessary for my purpose. My object is to give an idea of the whole development of one Lepas as accurately as possible, which seems never yet to have been done, as our whole know­ ledge of the development of this group consists of fragments, collected mostly in the same way in which B urm eister gained his information. The materials for this paper were obtained during our cruise from Japan to Sandwich (June to July 1875), as we went along the thirty-fifth degree of latitude, when first very curious Naupli, some of them 12 millims. long, were caught, which I identified at once with the nauplial form to which D oiirn has given the generic name of Archizoea In