( 208 ) 
fMonthly Microscopical 
L Journal, Oct. 1, 1869. 
NEW BOOKS, WITH SHOKT NOTICES. 
JReclierclies sur V embryogenie des CrustacSs. I. Observations sur le 
developpement de VAsellus aquaticus. Par Edouard Van Beneden, 
1869. — Although the valuable memoir which M. Van Beneden has 
been good enough to send us is not a book in the publishers' sense 
of the word, it is a work of so much importance that it justifies 
our noticing it under the head of Reviews. It is the reprint of a 
communication recently made to the Royal Academy of Belgium 
on an interesting species of fresh-water crustacean, and it expresses 
results of the highest value, especially in relation to the curious 
researches of Fritz Miiller and others in reference to those 
Nauplius forms which have so singular a bearing on Mr. Darwin's 
views. M. Van Beneden first sketches briefly the labours of those 
who have preceded him in the field, and he does so in that appre- 
ciative and kindly manner which is so characteristic of the genuine 
lover of scientific research. 
Fritz Miiller, in his 'Fiir Darwin,' a book some time since 
noticed in these columns, made known, under the name of larval 
membrane, larvenhaut, a structureless membrane, which in the 
Isopoda, and especially in Ligia, is formed round the embryo in 
the first stages of its development. This cuticular layer has the 
shape of an elongated sac, without lateral processes in the form of 
appendages, and should be considered, says the author, not as a 
dependent membrane of the ovum, but as the residue of tlie first 
embryonic moult. Now, M. Dohrn has recognized that there is 
found round the embryo of the young Asellus just such a mem- 
brane as that which Fritz Miiller has described in Ligia and 
others. M. Sars has also observed this, and has seen its relations 
to the antennae, which had escaped M. Dohrn, and which is a mor- 
phological fact of great import. MM Dohrn and Sars consider 
that the egg, at the moment it passes into the incubating pouch, is 
surrounded by two membranes, the outer of which represents the 
chorion, and the inner of which is a vitelline membrane. M. Dohrn 
has not tried to determine its significance, and he has simply termed 
the inner egg-membrane innere Eihaut. 
But the author has satisfied himself that at the moment of the 
egg's passing into the incubating pouch it is surrounded by a 
single membrane, which is directly applied to the vitellus. Soon, 
however, this separates, and leaves between it and the vitellus a 
transparent liquid. The single envelope on the recently-doposited 
ovum is what is generally styled the chorion. The other or inner 
membrane forms itself in the ordinary course of development after 
the egg has remained for some hours in the incubating pouch. 
What is the value and import of this envelope ? Is it part of the 
ovum, or is it rather an embryonic formation and the remnant of 
an embryonic moult which precedes the Nauplius moult ? 
