PERFORATIONS OF MARINE ANIMALS. 43 
before the spicules of the sponge were developed. Nassonow 
thought both chemical and mechanical agencies were employed, 
but he could not demonstrate the presence of an acid. 
The action of sponges on calcareous organisms in the ocean 
is a widespread and important one in disintegrating the in- 
numerable shells, corals, and nullipores on the floor of the sea, 
as well as the calcareous rocks at its margin; and whether this 
ceaseless destruction is caused by intrinsic or extrinsic agencies 
(e.g. by the aid of carbon-dioxide in sea-water), there can be no 
doubt as to the magnitude of the operations. It is, moreover, 
noteworthy that, so far as known, only calcareous media are 
affected by boring sponges. 
Burrowing in hard substances seems to be rare in the 
Ceelenterates, though Peachia, Edwardsia, and Cerianthus bury 
themselves in sand, clay, and mud. Prof. Haswell* mentions a 
minute Actinia which occupies cavities in a Cellepora much 
deeper than the length of the polyp itself. In most cases the 
orifices are furnished with a low projecting rim, and frequently 
two unite internally. This may, however, be an instance of the 
srowth of the Polyzoan round the Actinia, and not an instance of 
true perforation. Whether the case of the Anemones in holes of 
the rocks at Jamaica differs from the foregoing in so far as per- 
foration is concerned remains for further investigation. 
Turning to another and somewhat higher group of marine 
animals, viz. the Echinoderms, it is found that at least one 
species—the Purple Sea-urchin (Echinus lividus)—excavates con- 
siderable cavities, in which it lodges, in rocks—sometimes in 
rocks so hard as gneiss and granite. Authors assign to the teeth 
the main agency in the perforations, yet the cavities are some- 
what smooth. 
J. W. Fewkes,t after a careful examination of the perforations 
of Strongylocentrotus drobachiensis on the coast of Grand Manan, 
United States, considers that the excavations are due to the 
motions of the animals produced by waves and tide as well as to 
teeth and spines. He also thinks that they play some part in 
the formation of pot-holes. Prof. Cragin in the same volume,? 
* Proc. Linn. Soc. New South Wales, vol. vii. p. 608, 1882. 
+ ‘ American Naturalist,’ vol. xxiv. p. 1, 1890. 
t Ibid., p. 478. 
E 2 
