124 PROGBESS OF MICROSCOPICAL SCIENCE. 



proceeds or creeps along ; but so far as he can discover, they do not 

 assist the sponge in excavating in any way whatever, only that they 

 are the means by which the sarcode advances. Now it seems to him 

 that wherever the sarcode, or rather the investing membrane, touches 

 the shell, the latter shows an eroded surface ; the minute points and 

 pits can easily be seen with a quarter-inch objective. If one of those 

 fresh-bored holes be examined horizontally in good light, and even 

 with an inch objective, it will be seen that these holes are not smooth, 

 although they appear so to the unassisted eye, and even with a good 

 pocket lens ; but when carefully examined, a number of points and 

 angular processes are seen standing out into the hole in various 

 directions, showing at once that the hole had not been cut with any- 

 thing moved with a rotatory motion. He carefully examined these 

 h(l;s all the way down to their apex, and he finds the same appearance 

 all the way ; similar j^rojections of shell are seen all the way down. 

 1'he apices of these holes are not round, but are more or less angular. 

 Many of them have a triangular impression, and all of them show the 

 minutely-roughened surface, the minute points, and pits of an eroded 

 surface. Now he has carefully examined these sponges for some 

 erosive agents, the same as did Mr. Hancock ; but he has, with that 

 gentleman, not been able to detect any ; yet in his own mind he feels 

 certain that it is by the action of some agent of this kind that these 

 holes are eroded both by the annelids and sponges. Our not finding 

 an acid in these animals does not prove that they do not use, or sepa- 

 rate, or secrete, an acid or an erosive agent ; and he sees no reason 

 whatever for doubting, neither does he see any difficulty in believing, 

 in their decomposing the sea water, or separating carbonic acid from 

 it, and using it as soon as separated. By this means it is easily con- 

 ceived how these animals work, and it is also seen why we could not 

 discover the agent, for they kept none in stock, but mfjnufactured it as 

 they wanted it. He Olustrates his views by a very well-drawn plate, 

 showing the magnified borings. 



Unfortunately, however, this subject has recently had devoted to it 

 a paper,* by Mr. J. G.Waller, which is as full of exact information and 

 careful deduction as is possible. Mr. Waller, unfortunately for Mr. 

 Parfitt, proves beyond contradiction that this is really not a burrowing 

 sponge at all ; and his paper, though too long for insertion here, will 

 be read by those interested in the subject with advantage. His argu- 

 ments against the mechanical powers of the sponge seem to us to be 

 quite sufficient. In the section of an oyster-shell, of which he gives 

 a figure, we can see the burrows filled with a sponge, and at its distant 

 extremity, where is the latest growth of the sponge, we find the mem- 

 brane pellucid, with but few spicula. Going back into the older 

 portions, this membrane gets gradually more full of coloui", denser in 

 character, the spicula increasing in number, until they become almost 

 matted together. We then come to that part on the edge of the shell 

 where the laminse are wide and open, whose spaces, beside the burrows 

 and connecting with them, the sjionge has occupied, and here has 

 communication with the outer world. Hitherto the dermal membrane 

 * JJead before the Quekett Club, and published in its Jounial, January, 1872. 



