32 PROCEEDINGS OF THE 



grains of sand, pieces of shells, and masses of clay, held together 

 by means of a secreted mucus. 



The specimen which I now hand round, marked No. 1, probably 

 belonging to Maldane, is chiefly or wholly composed of clay. This 

 example is very poor, but it is the only one at present at my com- 

 mand. They are frequently met with, about an inch in diameter, 

 and twice that length, on mud bottoms in the Firth of Clyde; and, 

 although plastic, they are sufficiently firm and tough to bear con- 

 siderable strain without injury. The walls of this tube are hardest 

 next the annelid, and they increase in thickness by the action of the 

 exudation of the animal on the clay, becoming softer and softer 

 as they extend outwardly, until the line between the tube and 

 the soft mud in which it lies becomes imperceptible. In the 

 construction of this tube there is no display of ingenuity on the 

 part of the animal : a mass of stiffened clay, with an oblong cell 

 for the occupant, closed at one end, open at the other, and destitute 

 of all architectural design or beauty. 



No. 2, Terebella, is also a clay tube — a compact, long, smooth 

 cylinder, well defined, alike hard within and without, and which we 

 may therefore suppose was built from bottom to top, according to 

 the demands of the animal. This view is strengthened by observ- 

 ing a ring or joint near the top ; as this is not seen on other 

 parts of the tube, we may take for granted that this addition 

 had been in progress of completion at the time the animal was 

 captured, differing in this respect from No, 1, where the addition 

 appears to go on laterally. As extraneous matter enters into 

 the composition of the tubes, these animals may be fairly 

 looked upon as builders; and not without interest, when we 

 consider the nature of the thin, soft material out of which the 

 fabric has been consolidated. 



In Professor Thomson's report on the work of the "Challenger," 

 which appears in "Nature" of 23d Nov., 1875, he says: "We 

 sounded in 1,875 fathoms, with a bottom of bluish-grey clay, and 

 a bottom temperature of 1° 7c., forty miles to the south-east of 

 No Sima lighthouse. The trawl was put over, and it brought 

 up a large quantity of the bottom, which showed the clay was in 

 a peculiar concretionary state, run together in coherent lumps, 

 which were bored in all directions by an annelid of the Aphrodi- 

 tacean group. In many cases the annelids were still in the 

 burrows." May it not be possible that the cohesion of those 



