Miscellaneous. 285 



G. " On the Flowering of Plants, &c., in the Isle of Wight," by 

 Dr. T. Bell Salter. 



7. " List of Plants in flower, in the open air, in the neighbour- 

 hood of Ryde, Isle of Wight, in November 1855," by Dr. T. Bell 

 Salter. 



MISCELLANEOUS. 



On the Earliest Stages in the Development of Pelagia noctiluca. 

 By Dr. A. Krohn. 



In the December number of MuUer's 'Archiv,' Dr. A. Krohn 

 has given a remarkable positive proof of the existence amongst 

 the Medusae of a direct reproduction, without that intervention of 

 polype-like gemmiparous forms which constitutes what is called 

 the "alternation of generations" in these animals. This mode of 

 reproduction appears to be of exceedingly rare occurrence in the 

 MeduscB. It has hitherto been observed only in two species besides 

 the Pelagia noctiluca ; namely in Mginopsis mediterranea (by 

 Miiller), and in Trachynema ciliatum (by Gegenbaur). After 

 repeatedly observing young Medusce, which, from their general 

 characters, appeared to belong to the genus Pelagia, the author, in 

 the winter of 1853-54, met with individuals in a more advanced 

 state, which proved that they were the young of the common Medi- 

 terranean P. noctiluca ; and as in their earlier stage they agreed 

 perfectly with the young of Medusa aurita, which had not long 

 been detached from their polype-like nurses, he naturally concluded 

 that Pelagia noctiluca did not differ essentially in its mode of repro- 

 duction from the other Medusidce. Subsequently, however. Dr. 

 Krohn met with individuals in a far lower stage of development, the 

 youngest of which were of such simple structure that it appeared to 

 him they could not be far from the embryonic state, and he therefore 

 considered it important to ascertain in what form the embryo quitted 

 the egg. With this view he examined numerous females without 

 success, and was therefore compelled to have recourse to artificial 

 impregnation. His first attempts failed, but in the month of April 

 he succeeded in his object. Segmentation commenced in the ova 

 within a few hours after impregnation, and the first free embryo was 

 seen in the thirty-second hour. 



The embryos exhibited an unexpected form. They were always 

 considerably elongated, sometimes oval or oblong, sometimes very 

 long, slender, and cylindrical. They measured from |^ to 1 millim. 

 in length ; the anterior extremity is closed and rounded, whilst the 

 other appears more or less truncated, and exhibits an extremely small 

 round opening (the mouth), which leads into a well-marked roundish 

 cavity (the stomach), occupying the hinder third of the body. The 

 embryos appear semitransparent, in consequence of a delicate whitish 

 coat, which covers the limpid substance of the body. This is closely 

 set with fine short cilia, by the action of which the little creatures 



