PROaRESS OF MICROSCOPICAL SCIENCE. 
245 
generation in Leptodora hyalina* The development from the ordi- 
nary summer-eggs, as already described by E. P. Miiller, is with- 
out metamorphosis and like that of ordinary Cladocera, the young 
when excluded from the egg agreeing essentially with the adult ; 
while, according to Sars' observations, the young are excluded from 
the winter-eggs in a very imperfect condition, quite unlike the known 
young of any other Cladocera, and pass through a marked post- 
embryonal metamorphosis. In the earliest observed stage of the young 
of this form, the body is obovate, wholly without segmentation, the 
compound eye wanting, while there is a simple eye between the bases 
of the antennuloB, the swimming arms (antennas) well developed, and 
the six pairs of legs represented only by minute processes projecting 
scarcely beyond the sides of the body ; but the most remarkable 
feature is the presence of a pair of appendages tipped with cilia and 
nearly as long as the body, which are evidently homologous with the 
mandibular palpi of other Crustaceans, although these appendages 
have always been supposed to be wanting in the species of Cladocera. 
Two subsequent stages, gradually approaching the adult form, are 
described. The adults from the winter-eggs have no vestige of the 
mandibular palpi left, yet the simple eye — which is wholly absent in 
ordinary individuals developed from summer-eggs — is persistent, and 
thus marks a distinct generation. Three stages of the young from 
winter-eggs are beautifully figured upon the plate accompanying the 
memoir. This remarkable species has, still more recently, been made 
the subject of a very elaborate memoir by Professor Weismami of 
Freiburg,! who, however, had not observed the peculiar development 
of the winter-eggs. 
The ^ Challenger' Soundings. — Dr. Wyville Thomson says, in his 
report in the ' Proceedings of the Eoyal Society,' No. 156, that on 
the 11th of February, lat. 60°52'S., long. 80°20'E., and March 3, 
lat. 53° 55' S., long. 108° 35' E., the sounding instrument came up filled 
with a very fine cream-coloured paste, which scarcely effervesced with 
acid, and dried into a very light impalpable white powder. This, 
when examined under the microscope, was found to consist almost 
entirely of the frustules of diatoms, some of them wonderfully perfect 
in all the details of their ornament, and many of them broken up. 
The species of diatoms entering into this deposit have not yet been, 
worked up, but they appear to be referable chiefly to the genera 
Fragillaria, Coscinodiscus, Chcetoceros, Asteromphalus, and Dictyocha, 
with fragments of the separated rods of a singular silicious organism, 
with which we were unacquainted, and which made up a large propor- 
tion of the finer matter of this deposit. Mixed with the diatoms 
there were a few small Glohigerince, some of the tests and spicules of 
Eadiolarians, and some sand particles ; but these foreign bodies were 
in too small proportion to affect the formation as consisting practi- 
cally of diatoms alone. On the 4th of February, in lat. 52° 29' S., 
* Om en dimorph Udvikling samt Generationsvexel hos Leptodora^ Forhand- 
linger Vidensk.-Selsk,, Christiania, for 1873, p. 15, and plate. 
t Uber Bau und Lebenserscheinungen von Leptodora hyalina, Zeitschrift fur 
wissensch. Zool., xxiv., Sept. 1874, pp. 349-418, plates 33-38. 
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