EXCAVATORS. 35 5 



obtains access to the interior of the latter through 

 the more numerous tubes, and is expelled in quite 

 active currents from the wider tubes." l The general 

 sponge structure has already been detailed in the 

 chapter on sponges, and needs not repetition. 



Notwithstanding the doubts, which some writers 

 have expressed, of the possibility of sponges boring 

 into hard structures like coral, or the shells of mollusks, 

 we submit a few facts for consideration on the other 

 side of the question. " In 1871, a vessel laden with 

 marble, was sunk in Long Island Sound, and, accord- 

 ing to Professor Verrill, the boring sponge had pene- 

 tated the exposed parts of the blocks (in 1879), for a 

 depth of two to three inches from the surface. The 

 canals vary from one-fourth to a hundredth of an 

 inch, and less, in diameter ; the canals are coated 

 within with a thin film of dried sarcode of a brown 

 colour, which was orange coloured in life. Though 

 the sarcode is dried, the needle-shaped spicules are 

 plainly visible, under a one-fifth inch lens, and display 

 the form usually seen in the same species found on 

 the coasts of Europe. The specimen, which I have 

 seen, shows a series of large branching canals, which 

 connect freely with each other, in the most irregular 

 way imaginable ; moreover, the form of the canals, 

 in transverse section, is exceedingly variable, being 



1 "American Magazine of Natural History," vol. i. (1878), p. 54. 

 2 A 2 



