PERFORATIONS OF MARINE ANIMALS. 57 
Reeve, Bouchard-Chantereaux, Spence Bate, Darwin (for Ver- 
ruca), Ray Lankester, Parfitt and Schiemenz (for Natica). The 
latter has shown that the main agent in the small holes made 
in mussels and other shells by Natica josephina at Naples is the 
boring-sucker on the under surface of the proboscis.* Carazzi 
also describes the perforations of the date-shell (Lithodomus 
dactylus) as being due to chemical action, since its perforations 
are keyhole-shaped. It differs thus, he says, from Pholas. 
But this view will not explain the extensive perforations in 
wood (now specially before us), in aluminous shale, gneiss, 
sranite, sandstone, gutta-percha, resin, and wax. It is interest- 
ing, however, that shells and calcareous rocks are much affected 
by burrowing marine animals. Moreover, it is well known that 
even gentle friction on a wet calcareous surface—as by the feet 
and tails of Wallabys and allied forms at a drinking-place— 
will make a beautifully polished ‘‘ face” like that on the finest 
marble. 
Thompson and Necker, again, were of opinion that the boring 
action was a compound one—the result of a secreted solvent, 
aided by rasping; hence the solvent would require to vary with 
the nature of the rock attacked. 
Lastly, the very old idea of Sellius (and Deshayes), adopted 
by Gwyn Jeffreys, has to be considered, viz. that the perfora- 
tions are caused by a macerating or simple solvent action of 
the foot, and De Quatrefages thinks also of the mantle.t This 
would certainly avoid many of the difficulties caused by the 
previous theories, but it is doubtful if much support for this 
Opinion would be derived from the action in Sponges, Bryozoa, 
Annelids, Gephyreans, and Cirripedes. It has also to be borne 
in mind that the crustaceans which burrow in wood do so only 
by mechanical means, and so with certain burrowing insects. 
Leaving the subject of the means, which would appear to be 
* Mitt. Zool. Stat. Neapel, Bd. x. p. 152, Taf. 11. 
+ This recalls the statement that if a plant be permitted to grow on 
polished marble an outline of the root is marked on it, a result supposed to 
be due toan acid secretion (chlorhydric) of the root-hairs. Prof. J.H. Storer, 
indeed, endows the rootlets with what he terms a power of osmotic dissocia- 
tion, and he would extend the same explanation to the boring animals (Amer. 
' Jour. Sc. 28, pp. 58-61, 1884). 
Zool. 4th ser. vol. XII., February, 1908. F 
