ACTINIJB AND OTHER ACTJNOID POLYPS. 33 



700 diameters. Figure 1 represents one of the lasso-cells of 

 the Actinia, Corynactis viridis, with its lasso coiled up within, 

 its actual length is about a 350th of an inch. Figure 2 is the 

 same with the lasso out, though less than half of the long 

 thread is shown. Figure 3 is the lasso-cell of the polyps of a 

 European coral, the Caryophyllia Smithii. It differs from 

 figure 1 in having the basal part of the lasso within the cell or 

 sheath strait and stout ; it is this part which makes the first 

 portion of the extended lasso. A view of part of the latter is 

 represented in figure 4, and of the extremity of the same in 

 figure 5. The lasso-cells in the above species are from a 240th 

 to a 360th of an inch in length. In the Metridium margina- 

 tum, an American Actinia occurring along the coast of the Uni- 

 ted States, north of New York, the length of one of the lasso- 

 cells, according to Dr. Leidy, was about a 400th of an inch, 

 and the character of the extended lasso was much like that of 

 figure 4. The lower part of the lasso, for a length l£ times 

 or more longer than the cell or sheath, is usually thickened, 

 and sometimes slenderly spindle-shaped, while the rest is an 

 even slender thread ; and the thickened part and sometimes 

 all the rest, as above shown, is spirally wound by a slender 

 line, sometimes elevated, set with short hairs or bristles. The 

 thread-like portion may be wanting or very short. The lasso 

 is often twenty times as long as the cell or sheath, and occa- 

 sionally forty times ; but if the thread-like part is absent, only 

 one and a half to two times. 



A lasso-cell once used is afterward worthless ; for the tube 

 cannot be returned to the sheath. But those thus expended 

 are not missed, as the polyp has indefinite supplies of such 

 weapons, and also ready means of refurnishing itself. 



Figures 6, 7, 8, 9, 10, on the preceding page, illustrate 

 different stages in the development of a lasso-cell (fig. 10) 



