20 The American Naturalist. _ [January, 
is any need of a complicated buccal apparatus such as is found in 
Strongylocentrotus. One is even tempted to regard the lantern 
in Echinarachnius as a rudimentary organ which has lost its 
functional importance.” 
While it is next to impossible to say how much or how little 
of the excavation is due to any one of the three means of wear- 
ing away of the rock, the teeth, spines, and wave „action, we can 
safely conclude that the most important factor in this work is the 
dental apparatus. Next in importance are possibly the spines, 
while last of all comes that work done by the rolling about of 
the sea-urchin due tothe motion of the water. To the general 
proposition advanced by John, we might also add that there is 
evidence that the time which has elapsed between the inception 
of the sea-urchin’s work in excavation and the present condition 
of the cavities is probably much larger than the life of the indi- 
vidual which now occupies it. In an interval between two occu- 
pants the interregnum may have been filled out by effective 
grinding out of the cavity by the motions of the test of the former 
occupant, or by fragments of the spine, the teeth, or other hard 
parts of the dead animal which has left this heritage as a means 
when moved by the water to grind out the excavation for its 
successor. 
After a somewhat extended discussion of the views of others, 
John gives as his conclusions in regard to sea-urchin excavations 
the following summary: 
“ Die in den Gesteinen gefundenen und von Seeigeln bewohn- 
ten Höhlen rühren von diesen selbst her. Der Echinus erzeugt 
seine Wohnstatten mittelst seines Kauapparates und sekundär mit 
Hilfe der Stacheln durch rotierende Bewegung. Er bohrt sich 
solche Hohlungen, um einen Schutz gegen das brandende Meer 
zu haben. 
“ Die Kalkalgen, welche die von Seeigeln bewohnten Gesteine 
bedecken, lagern sich mechanisch auf das Gestein und haben 
32 It seems to the writer capable of proof that the fiat sca-urchms are structurally lower 
mara their internal = goni oa aa rat called “ round S Still that 


‘dale o and this does not seem the plaze to present arguments in its support, or to combat 
which might readily be made to 
