iSi Mr. A. Hancock on the Excavating Sponges, 



occupied by Clionce there are numerous circular orifices opening 

 at the surface of the shell or stone containing the parasite; 

 now the papillse or oscula of the sponge, communicating with 

 the water, always protrude through these apertures, and invari- 

 ably correspond to them in size, number, and position, leaving 

 no orifice unoccupied, and exactly fitting each, whether there be 

 upwards of two hundred to the square inch, as in C. vastijica, 

 or only about twenty-five or less, as in C. celata. How are we 

 to account for such a fact as this, if it be maintained that these 

 orifices were drilled by worms ? Are we to consider that this 

 complete correspondence between these parts of the sponge and 

 the orifices is a mere chance coincidence — wonderful, indeed, if 

 true ? or that the worm made the openings purposely, in strict 

 accordance with the requirements of the sponge that on some 

 future day might take up its abode in the deserted excavation ? 

 or is it that the sponge has the power of modifying the position, 

 number, and size of these important organs to meet the circum- 

 stances of its usurped home ? The first two propositions cannot 

 be entertained for a moment, and the last is contradicted by the 

 fact that C. vastifica is never found with few and large papillae, 

 like C. celata ; nor in the latter species are they ever very nu- 

 merous and minute, as is the case with the former. And, indeed, 

 the arrangement, size, and number of the papillae are good spe- 

 cific characters throughout the genus. 



If we now refer to what is stated in my former paper on the 

 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 

 inquirer that Cliona excavates for itself its abode in hard calca- 

 reous bodies :-— 



1. That the sponge, when examined in a good state, is always 

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

 ramification. 



2. That the excavations are as frequently in limestone as in 

 shell. 



3. That no worm has been found that can be pronounced to 

 have made these excavations, and that worms are rarely or never 

 taken in them. 



4. That these excavations have no resemblance whatever to 

 the burrows of worms. 



5. 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. 



6. That ClioncB with the papillae gf the same size, number. 



