1890.] Excavations by Sea-Urchins. 9 
We have members of almost all the lower groups of animals, 
as sponges, annelids and other worms, mollusks and crustaceans, 
all of which are endowed with boring habits. The excavating 
habit possessed by the sea-urchin may belong to the same cate- 
gory as that of these animals, and it may be a voluntary act for 
self protection or other purposes. There is, however, this very 
interesting fact pointed out by others in relation to the boring 
sea-urchin, in which it seems to differ from those already men- 
tioned. The habit of excavating seems to be one which is 
limited to individual sea-urchins which live in certain exposed 
positions, where the tides are very high. Thousands of speci- 
mens of sea-urchins on rocks where there was not a visible sign 
of excavating can be found, and those echinoderms which are 
below the wash of the tide, as well as some in its force, exhibit no 
manifestation of this power. These facts lead me to ask if it is 
not possible that there are influences in environment or in phy- 
sical forces acting upon them which make certain individuals an 
involuntary agent in boring. Or is it not probable that we 
may find the excavating power due in part to the action of the 
sea itself. It is in other words possible that the force which ex- 
cavates these geodes is somewhat similar to that exerted in the 
case of the formation of the geologic phenomenon known as 
“pot-holes.” The living body of the sea-urchin might occupy 
the same relation to the cavity in which it lies that the inert stone 
does to the pot-hole in which it is often found, and which it 
played an essential part in creating. The fact that beautiful 
examples of pot-holes can be seen worn out of the solid rock on 
the adjoining island of Grand Manan, not far from the sea-urchin 
excavations, has suggested this explanation, which certainly has 
much to recommend it. We may, if we adopt this theory as a 
part of the explanation, regard the echinoid body clothed with its 
spines as an involuntary agent moved about by the waves, 
slightly perhaps, yet moved enough to wear out by its attrition 
in course of time the solid substance of the rock. The spines, 
teeth, and possibly the body itself may thus exert a wearing 
action capable in time of making an excavation into the solid 
rock. This explanation would furnish good reason for the very 
