Miscellaneous. 411 
of the Turride, from which we must at the same time remove the 
genus Corydendrium, which Allman had included in it on account 
of the uncertainty which still exists to its reproductive organs. 
In regard to the habitat of this form, I may observe that my 
specimens were found in a very different condition from those of 
the first specimen described. Weismann had a colony which had 
been taken from a depth of 70 to 80 metres. On this account he 
refers to Dendroclava Dohrnii as a form living at great depths, 
My specimens on the contrary had been taken off the coasts of 
Nisida, and it is only necessary to glance at a bathymetric map of 
the Gulf of Pozzuoli to see that the island of Nisida is surrounded 
by waters of very inconsiderable depth.—Bolletino Scientifico, N. 3 
e 4, Anno 1891. 
On the Development of Bythinia tentaculata. By Dr. R. v. 
Eruaneer, of the Heidelberg Zoological Institute. 
Having been occupied for a long time with the embryology of 
Gastropods, I thought it desirable to test upon another Prosobranch 
the observations which I had made upon Paludina vivipara. For 
this purpose Bythinia tentaculata appeared to me to be most adyan- 
tageous, since all the stages of development are to be had in any 
quantity, and the youngest are very suitable for sections on account 
of their relative size. Another circumstance strengthened me in 
my intention. Bythinia has already been the subject of a lengthy 
paper by P. Sarasin *, whose results were by no means to be recon- 
ciled with those which I had attained in the case of Paludina. The 
sequel will show that in almost all important points I have arrived 
at precisely opposite views to Sarasin, and that the development of 
Bythinia possesses a great similarity to that of Paludina. 
After the expulsion of the directive vesicles the segmentation 
proceeds in the manner which is typical for the majority of Gastro- 
pods, and conforms closely to that of Planorbis and Neritina. 
Immediately after the division into two it becomes evident that the 
cells of the germ do not all divide simultaneously, but that the 
macromeres which are first formed gradually give rise to a large 
number of micromeres. I traced the segmentation as far as the 
stage with forty-eight cells; I did not succeed in following it 
further, on account of the excessive number of segments. By the 
time this stage is reached a segmentation-cavity of considerable size 
has been developed, which soon afterwards acquires its greatest 
dimensions. At the vegetative pole the four macromeres only are 
present, while the micromeres, which give rise to exclusively ecto- 
dermal elements, gradually diminish in size from the vegetative to 
the animal pole. The macromeres exhibit precisely the same 
arrangement as the corresponding cells in Planorbis. The anterior 
and posterior are in contact with one another, forming a sharply 
* P. Sarasin, ‘Entwicklungsgeschichte der Bythinia tentaculata’ In- 
augural-Dissertation, Wiesbaden, 1882, 
