42 THE ZOOLOGIST. 
present known, sponges bore only in calcareous substances, vz. 
in limestones, shells, nullipores, and corals, but their exact 
method of operating is still involved in mystery. Prof. R. Grant 
seems to have been one of the first to notice that Cliona formed 
its own tunnels, and Duvernoy followed him in describing a 
foreign species. Nardo,* again, subsequently gave an account 
of the perforations of the shells of mollusks, and Michelin 
further pointed out the dendritic pattern of such excavations. 
McCalla (1849) also knew that Cliona was destructive to shells. 
Dr. Bowerbank, the able author of the ‘British Sponges,’ held 
that they never perforated either rocks or shells, but only took pos- 
session of cavities bored by other forms, and that he had found the 
sponges only partially filling the chambers in the calcareous rocks 
on the southern coast. Some hold that the soft animal jelly or 
protoplasm of the sponge is the agent, while others, such as the 
late Albany Hancock, maintain that it bores by aid of its spicules. 
One or two, again, like Dr. Bowerbank, have insisted that the 
sponges do not perforate, but inhabit the galleries of other forms. 
Thus, some years ago, an able zoologist considered that the 
so-called boring sponges only occupied the tubes of annelids, 
and forwarded many specimens with a view to substantiate this 
opinion. From dredgings off the Channel Islands a very thin 
shell (lower valve of Anomia ephippiwm), in which translucent 
medium a Cliona had established itself, was forwarded to the 
zoologist. When held up to the light the beautiful dendritic 
patterns made by the sponge were clearly outlined, the oscula of 
the sponge, moreover, projecting from the widened areas. Now 
this shell was so thin (much thinner than that of Placuna 
placenta) that no known annelid could form a lodgment in it. 
The zoologist did what, perhaps, was most judicious, viz. 
avoided all subsequent allusion to the matter. A considerable 
time ago the subject was investigated by Nassonow,t who culti- 
vated young boring sponges on thin transparent calcareous 
lamelle. The larve, after a free stage, settled on the plates, a 
rosette-like mark appeared, and the sponge gave off thin pro- 
cesses, which passed into the substance of the plate and followed 
the contour lines of the rosette. This penetration happened 
'* © Atti degli Scienziati Italiani,’ p. 161, Pisa, 1839. 
+ Zeitsch. f. Wiss. Bd. 39 (1888), p. 295. 
