1889.] Zoology. 729 
Near by this pool there are others with sea-urchins, apparently under 
the same conditions, where there is no sign of excavations, and long 
stretches of coast on the neighboring island, where the rock is perfectly 
paved with sea-urchins, show no attempt on the part of these animals 
to form even the slightest depression in the rock surface. The exis- 
tence of these excavations is exceptional even in the Black Ledges, 
and the phenomenon is thought to be rare even on Grand Manan. 
Except that possibly the spines about the mouth were stouter than 
those found on sea-urchins which had not made the excavations, there 
is nothing to distinguish the inhabitants of the excavations from their 
neighbors. In no case was it found that the sea-urchins had sunken 
into the rock below its surface level, nor were the animals in any in- 
stance larger than the entrance of the cavities, or unable to escape 
from the holes in which they were found, as seen in so many specimens 
It is said by fishermen that our sea-urchins bore into the birch 
stakes used in building weirs, but I was unable to observe this phe- 
nomenon. In some places, however, the back and outer rings of the 
wood fibre was removed, apparently by them. 
The one explanation of this work of the sea-urchins which an ex- 
amination of the cavities suggests, is that they bury themselves in this 
May for protection, or for a more effective way of clinging to the cliff", 
but if such is the true explanation, why is the habit so localized and 
The method by which the cavities are hollowed out of solid rock is 
also a prolific subject for a theory, and many explanations have been 
advanced. I incline to believe that it is simply the effect of a me- 
chanical erosion in the case of the Grand Manan specimens which 
The rate of wearing of the holes is very slow, and there is reason to 
believe that many sea-urchins were concerned in the ])rodnction of 
is i^robably the last of a series of several members, and the same may 
be true even when the sea-urchin is larger than the entrance to the 
chamber in which it lives. When the sea-urchins are removed from 
them, so that there is little change in their appearance. The new 
denizens take up the work where their predecessors left off. This con- 
