82 



THE AMERICAN MONTHLY 



[May, 



to be still a matter of mere conjecture 

 requiring confirmation by careful 

 study and observation. My attention 

 was called to this subject some time 

 ago by the published reports of the 

 discussions in the Quekett Club, of 

 London, respecting the boring pow- 

 ers of this sponge, from which it would 

 appear that very little was positively 

 known, but that many good grounds 

 existed for believing, that the bur- 

 rows in which Cliona is found, may 

 have been excavated by annelids, or 

 some other of the numerous shell- 

 borers and lithodomes, that are well- 

 known to possess the necessary tools 

 for mining such hard bodies. 



The following are some of the prin- 

 cipal reasons offered by Bowerbank, 

 and more recently by other natural- 

 ists, for considering Cliona merely a 

 ^' parasite " in the burrows which it 

 occupies. 



First: That the excavations could 

 not be done mechanically with the 

 spicules, was shown by the absence 

 of muscular or contractile power in 

 the sponge, or any indications of wear 

 of the spicules, as would be the case 

 if they were used as tools for abrad- 

 ing such hard bodies; and the sup- 

 position that the sponge secreted some 

 acid fluid that enabled it to dissolve 

 calcareous bodies and thus penetrate 

 them, was pronounced improbable 

 from the fact that upon chemical ex- 

 amination no acid could be detected. 

 Second: That in certain specimens 

 examined, the sponge was found to 

 occupy only the channels near the 

 outer surface; and did not penetrate 

 to their extreme interior limit, as 

 would necessarily be the case if it 

 had made the burrows itself. 



Much stress was also placed upon a 

 peculiar character of these burrows, 

 which, it was thought, showed conclu- 

 sively that they had been cut by the 

 concentric strokes of a hard tool, like 

 the jaws of an annelid. This is shown 

 in fig. 27, which represents the appear- 

 ance of the burrows in a thin section 

 of shell, as seen under the micro- 

 scope. The holes through such sec- 



tions, instead of being bounded by 

 continuous and regular curves, as it is 

 claimed they would be if excavated by 

 a solvent, present a series of irregular, 

 concave depressions as if abraded or 

 gnawed by some borer, much smaller 

 than the canals excavated — the arc of 

 a circle in these depressions generally 



Fig. 27. 



representing, for the excavator, a dia- 

 meter of something less than the ■^\^ of 

 an inch. It is also claimed that the 

 burrowing larva of Scolytus, of corres- 

 ponding size, was known to excavate 

 in a similar manner. These eviden- 

 ces, coupled with the distinct asser- 

 tion " that there is not on record any 

 observation which proves the sponge 

 to be an excavator," would seem to 

 make a very strong case against Cliona 

 as a borer. 



A careful study of the literature of 

 this subject, which is quite volumi- 

 nous, extending over a period of at 

 least forty years, convinced me that 

 there was one weak point in the 

 method which, as far as I could dis- 

 cover, had characterized all observa- 

 tions, and which consequently invali- 

 dated, to a great extent, the conclu- 

 sions on both sides. This was, that 

 those observations had been made 

 upon dried specimens ; or, as one au- 

 thor distinctly mentions, upon the 

 live sponge occupying old shells and 

 rocks. It occurred to me that a care- 

 ful study of the live sponge occupy- 

 ing, and working upon, the shells of 

 healthy, living and growing mollusks, 

 might present some features or evi- 

 dence, for one side or the other of 

 this argument, that had hitherto been 



