344 MR. ALBANY HANCOCK OX 



subject already quoted, and at the same time take into account 

 what is advanced on the present occasion, we shall find that the 

 following facts seem to be sufficiently demonstrated. And they 

 certainly appear cogent enough to satisfy the most scrupulous 

 enquirer that CKona excavates for itself its abode in hard calcare- 

 ous bodies. 



First. — That the sponge, when examined in a good state, is 

 always found to fill every part of the excavation, even to the 

 minutest ramification. 



Secondly. — That the excavations are as frequently in limestone 

 as in shell. 



Thirdly. — That no worm has been found that can be pro- 

 nounced to have made these excavations, and that worms are 

 rarely or never taken in them. 



Fourthly. — That these excavations have no resemblance what- 

 aver to the burrows of worms. - 



Fifthly. — That the surface of the excavations inhabited by 

 Cliona is always shagreened or punctured in a peculiar manner ; 

 while that of the burrows of worms is always smooth. 



Sixthly. — That Clionm, with the papilla? of the same size, 

 number, and arrangement, and with the same kind of spicula, 

 always occupy similar burrows. 



Seventhly. — That the oscula or papilla? always correspond in 

 size, number, and position to the external orifices in the surface 

 of the shell or stone enclosing the sponge. 



Eighthly. — That Cliona has been traced through every stage 

 of growth, from the microscopic gemmule adding branch after 

 branch and lobe to lobe, to the fully developed sponge, excavat- 

 ing step by step its complicated abode in sound, transparent shell. * 



Cliona undoubtedly works out the cavities that it inhabits, 

 whether mechanically or otherwise. Whatever the process may 

 be, the difficulty in believing that a sponge, even if deprived of 

 all mechanical agency, can burrow into hard substances, is much 

 lessened since I first wrote on the subject. It has recently been 

 ascertained that some of the Polyzoa bury themselves in hard 

 calcareous bodies ; as does also Lagotia viridis, a minute and 



* Ann. and Mag. of Nat. Hist., 2nd Series, Vol. Ill, p. 327. PI. IV, fig. 4. 



