183 
HOW HEKMIT CRABS GET POSSESSION OF THEIR 
SHELLS. 
By ALEXANDER AGASSIZ. 
W HILE tracing the development of one of our species of 
Hermit Crabs, I raised from very young stages a number 
of specimens till they reached the size when they need the pro- 
tection of a shell for their further development. I was of 
course curious to see how they would act the first time when 
supplied with the necessary shells. For this purpose, a number 
of shells, some of them empty, others with the animal living, 
were placed in the glass dish with the young crabs. Scarcely 
had the shells reached the bottom before the crabs made a rush 
for the shells, turned them round and round, carefully examin- 
ing them, invariably at the mouth, and soon a couple of the 
crabs decided to venture in, which they did with remarkable 
alacrity; and after stretching backward and forward, they 
settled down into their shell with immense satisfaction. The 
crabs who were so unfortunate as to obtain for their share living 
shells, remained riding round upon the mouth of their future 
dwelling ; and on the death of the mollusk, which generally 
occurred soon after in captivity, commenced at once to tear 
out the animal, and having eaten it, proceeded to take its 
place within the shell. 
It is of course very difficult to apply to Invertebrates many 
of the laws of natural selection, and thus far we know so little 
of the habits of most of our marine animals that it is idle 
I to speculate upon the effect of causes which may effectually 
i modify the life of higher animals. In the case above men- 
tioned there is no possible connection between the embryo and 
the parent to account for the young having learned from the 
former the use of the shell and its value for his existence. 
We can therefore only explain the faculty of performing the 
act as inherited, or else as a simple mechanical act rendered 
necessary by the conditions of the young hermit crab. This 
latter seems the more probable case from the nature of the test 
