214 THE ZOOLOGIST. 
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. Rarefyiug 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 pressure, be 
either forced downwards or upwards, and thus they are in unstable equili- 
brium as to level. As to position, the bladder being in the ventral region, 
the centre of gravity is above the centre of pressure, so that fishes are 
always threatened with inversion; and, indeed, they take the inverted 
position when dead or dying. ‘This double instability forces fishes to a 
continual gymnastic movement, and doubtless helps to render them strong 
and agile. ‘The most agile of terrestrial animals are also those which have 
least stability. 
UnusuaL Weicut or a Cras.—On April 9th a very large Crab was 
brought to my house that I might see it, but I was unfortunately from 
home at the time. I have to-day (April 11th) seen the man who brought it 
to me, and whom I know to be respectable and trustworthy, and he tells 
me it was taken in a trawl, and was weighed on board the trawler in his 
presence, and that it turned the scale at sixteen pounds avoirdupois weight. 
I write this with the reservation that I believe it to be true, but that 
I cannot vouch for it to my own knowledge. It is four pounds heavier than 
the heaviest I ever saw.—THomas Cornisu (Penzance). 
[Mr. Carrington informs us that the largest Crab he ever heard of was 
a Norwegian one, and weighed eleven pounds. Bell, in his ‘ History of 
British Stalk-eyed Crustacea,’ states that a weight of twelve pounds is 
occasionally attained.—Ep.| 
Potsonous QuaLITIES OF THE StTaR-FIsH.—On February 18th I picked 
up, on the shore here, a fine specimen of the Sun-star (Solaster papposa), 
which I took home and laid on my study fender to dry. On the 20th, 
during my absence from the room, two favourite cats of mine came in and 
ute the Starfish. They were discovered almost in the act, and nothing 
was thought of it at the moment. In about ten minutes, however, the 
smaller cat, which was about half-grown, was violently sick, and in less than 
a quarter of an hour was dead. Soon after, the other cat, which was full- 
grown, suddenly began to scream piteously, and was also sick. It soon 
became unable to walk or stand, and died (about two hours after eating the 
