= 
1887] Embryology. 293 
and soon. These and kindred questions will evidently be fairly 
dealt with in Professor Haddon’s treatise, judging from the ad- ° 
vanced sheets of the first forty: pages of the work, which the 
editor of this department has had the opportunity of examining. 
The work will evidently be up to date, and many points upon 
which the earlier authors were uncertain will be cleared up. 
e newer views as to the origin of the middle germinal layer 
will be presented, and Duval’s discoveries in the development of 
the chick will receive the attention they deserve. The more 
recent discoveries in mammalian embryology and the discussion 
of karyokinesis, so far as it relates to embryology, will also find 
a place. n the whole, it may be said that this work is a timely 
one, which will be welcomed by all who are alive to the signifi- 
cance of the great issues of the embryological science of the 
future. The author and publisher are also to be congratulated 
upon the many new figures introduced,—many of them original, 
—and the excellent typographical appearance of the pages. The. 
style of the author is clear and terse, a matter that is not always 
as well attended to by the authors of elementary text-books as is 
desirable, in spite of the remarkable precedents before them in 
the clearly-written a manuals by such writers as Hux- 
ley, Clifford, and Tyndall. 
Development of Mysis.—Nusbaum gives (Biol. Centralblatt, 
vi. 663) a preliminary account of his observations on the develo: 
ment of Mysis. According to him the egg is surrounded by a 
blastema, and has the nucleus lying at the formative pole. The 
result of the first segmentation is to form two cells, one of which 
forms the blastoderm while the other sinks into the yelk. The 
larger central cells of the blastoderm later divide and give rise to 
cells which sink beneath the blastoderm, and together with the 
roduct of the first segmentation just mentioned are called 
“ Vitellophags.” After this process the rudiments of the embryo 
appear,—a caudal area from which extend forward the ventral 
bands, which diverge like a V and terminate in the oval cephalic 
lobes. Now, according to Nusbaum, a shallow invagination 
takes place in the caudal area, and the invaginated cells under- 
going a rapid proliferation form a solid entoderm. Behind this 
point the abdomen now grows out. The mesoderm, says Nus- 
baum, arises as two bands from the ventral bands. The vitello- 
phags at first lie just beneath the germinal area, but later they 
sink deeper into the i and as their name implies they feed 
upon the yelk. Nusbaum has some comparisons with the de- 
velupment of various ea which he thinks are similar in 
the formation of the germinal seng and his vitellophags he 
compares to similar cells in Scorpio and Oniscus, as well as to 
~ phagocytes of Metschnikoff. He ass describes a dorsal organ 
ch appears at first as a paired ectodermal thickening, the 
