274 



that no sponge could do it. It had not been mentioned that there were 

 three theories as to this matter — one referred the action to that of some 

 solvent — another thought it due to the action of a soft living substance, 

 whilst a third ascribed it to the action of a hard substance. He had some 

 experience of the action of acids, and also of a graver, and it was quite 

 certain that a line, however light, made by a solvent, was never like that by 

 a graver, and could not be confounded with it, and it was quite certain that 

 a soft substance produced its special characteristics upon the substance on 

 which it acted by rendering every sharp angle and detail perfectly smooth 

 and obliterating distinctive form altogether. The well known example of 

 the toe of the statue of St. Peter at Eome being completely worn down to 

 a mere knob by the repeated osculations of the faithful for centuries, waa 

 an instance of the last-named kind of wearing away. Give the requisite 

 time, and the wearing away could be done by a soft body, but the nature of 

 the resulting effect ought to be such as to make it quite easy to say whether 

 it was done by a hard or by a soft substance. 



Mr. Chas. Stewart, whilst disclaiming to be an authority upon the subject, 

 said he must certainly join issue with Mr. Waller on the question of the 

 boring sponges. In looking for the most probable explanation, what did 

 they find in the facts themselves to guide them in their opinion ? They 

 found that rocks and calcareous substances were channelled out in the 

 manner described and figured, and that sponges were inserted in these ex- 

 ceedingly fine orifices, and the question was whether these minute perfora- 

 tions were made by marine annelids ? lie thought that they were much 

 more likely to have been done by the sponges themselves, and it had been 

 suggested that it was accomplished in one of three ways. Firstly, the 

 action might be of a cutting nature like that of a graver, but this he thought 

 to be highly improbable ; the second idea was that the spaces were eaten out 

 by some acid excretion which decalcified the structures with which it came 

 into contact ; and the third mode was by what might be called a colloidal 

 action. When they examined the surface of the materials which had been 

 acted upon, they found it was not a smooth one by any means, but it was 

 eaten out into various concave depressions. Now when they looked in 

 other directions they found that there were other substances which were 

 eaten away in an almost precisely similar manner. If a dead bone were left 

 surrounded by living tissues it would be actually thus eaten away by the 

 soft granulated tissue around. The same process was going on in the case 

 of ordinary bone, for they found numbers of holes regularly excavated 

 in the bone tissue which were known as Haversian spaces, and which 

 were due to the action of the so-called bone destroying cells. Here, 

 then, was an instance in which depressions were produced with "conT^ 

 parative rapidity by the action of soft substances, and it seemed to him 

 on looking into a section of rock supposed to be perforated by a sponge 

 that they had there an appearance identical with that of an Haversian 

 space ; and he thought that the process by which these soft osteoblasts 

 excavated the bone mipht be applied in the case of rock^ and shells. 

 Certainly no annelid could do it. With regard to the position of the 



