22, TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
head always facing the one way in order that they may fit 
into the depressions. 
It is not yet known by what sense the limpets are able 
to find their way back to their roosts when they leave them — 
in search of food. It is certainly not by sight, as the eyes 
are very simple and imperfect. It has been proved by 
experiment that it is not by smell; while taste, and feel 
can scarcely help. There may be a sense of direction 
different from anything we know of in our own experience; 
but what the exact method 1s by which the limpet finds its 
way about, can go back the way it has come, and can 
recognise 1ts own roost amongst a number of similar 
neighbouring depressions, has still to be discovered. 
Now for the interest of the present specimen. It is so 
closely moulded to the iron bar that I am of opinion that 
it could not have been in the habit of leaving its home and 
prowhng about. In the first place, the bar was short, and 
was loose, and free to roll about, and it would be very 
difficult for a crawling snail-like animal such as the limpet 
to cross from the bar to the rocks even if its support was 
stationary, but if, as seems likely, the bar was being rolled 
about by the waves, one does not see that it would be 
possible for the limpet to re-find its roost, if it ever left it. 
Possibly, however, as some think, the limpet never loosens 
its hold when covered by the tide. This would remove 
the difficulty partly but not wholly. Then, in the second 
place, the shape of the shell in this specimen is such that 
I do not see that the animal could crawl over the rocks, or 
could occupy any position other than that on the bar in 
which we found it. 
After examining this specimen, I looked carefully at 
the limpets scattered over the rocks, and found several 
in which the animal was situated at the bottom of a 
deep pit, from which it would be very difficult, if possible 
