898 General Notes. [ December, 
long appendage it carries. He then examines the evidence de- 
rived from a study of the muscular and nervous parts, and from 
the phenomena of development. The work is thoroughly well 
done, but of such a nature that it-cannot be abstracted. The two 
plates evince excellent artistic skill. 
THE SWIMMING-BLADDER OF FisHEs.—In a recent note to the 
Paris Academy, Prof. Marangoni gives the results he has arrived 
at in a study of the swimming-bladder. He states, first, that it is 
the organ which regulates the migration of fishes, those fishes that 
are without it not migrating from bottoms of little depth, where 
they find tepid water; while fishes which have a bladder are such 
as live in deep, cold water, and migrate to deposit their ova in 
warmer water near the surface. Next, fishes do not rise like the 
Cartesian diver (in the well known experiment), and they have to 
counteract the influence of their swimming-bladder with their 
fins. If some small dead and living fishes be put in a vessel three- 
quarters full of water and the air be compressed or rarefied, one 
finds in the former case that the dead fish descend, while the living 
ones rise, head in advance, to the surface. Rarefying has the 
opposite effect. Fishes have reason to fear the passive influence 
due to hydrostatic pressure; when fished from a great depth, their 
bladder is often found to be ruptured. Thirdly, the swimming- 
bladder produces in fishes twofold instability, one of level, the 
other of position. A fish, having once adapted its bladder to live 
at a certain depth, may, through the slightest variation of pres- 
sure, be either forced downwards or upwards, and thus they are 
in unstable equilibrium as to level. As to position, the bladder 
being in the ventral region, the center of gravity is above the 
center of pressure, so that fishes are always threatened with in- 
version; and, indeed, they take the inverted position when dead 
or dying. This double instability forces fishes toa continual gym- 
nastic movement, and doubtless helps to render them strong and 
agile. The most agile of terrestrial animals are also those which 
have least stability. 
Zooocicat Norr’—From his study of the mollusks of the 
Challenger expedition, the Rev. R. B. Watson concludes that 
