198 THE birds' heads. 



parallel sides, filled with the purest sea-water, and 

 put the whole on the stage of your microscope with a 

 power of not more than 100 linear, at least for the 

 first examination ; — I greatly mistake if you will not 

 confess that the intellectual treat obtained is well 

 worth, aye, ten times more than worth, all your 

 trouble. 



The cells of the Bird's-head Coralline are oblong, 

 shaped somewhat like a sack of com, with a spine 

 ascending from each of the upper comers. (See figs. 

 2 and 3.) Each stands on the summit of its prede- 

 cessor in the same row, and side by side with those of 

 its fellow rows, in such an order that the top of one 

 cell comes opposite the middle of the one beside it. 

 The top of the cell is rounded and appears imperforate, 

 but we shall presently find an opening there. The 

 broad side that faces inwardly has a large elliptical 

 transparent space occupying nearly its whole surface, 

 which, from its well-defined edges, I was long tempted 

 to think, was really a great aperture, though delicate 

 manipulation appeared to give a very subtle surface 

 to it ; this, as I subsequently found, is covered with a 

 very thin and elastic membrane, and answers a pecu- 

 liar end. Just below one of the spines that crowns 

 the summit of the cell, on one of the edges, x-ather on 

 the interior than on the exterior, is situated a little 

 tubercle, to which is attached, by a very free joint, a 

 bird's-head process, in all essential particulars agree- 

 ing with that of Cellularia cilitata which I have 

 already described. The lower mandible in this case 

 is, however, set farther back, and the upper is desti- 

 tute of those tooth-like serratures that characterize it 



