ITS MODE OF GROWTH. 133 



son,) the outline being nearly half a crescent. The 

 increase of the branch is effected by a cell growing 

 out of the upper and outer rim, the aperture being 

 obliquely truncate ; from the outer rim of this 

 another grows ; and so on in succession for an indefi- 

 nite number. But when a new branch is to be formed, 

 the first cell of which- it is to be composed shoots 

 from the inner and lower rim, and the cells then face 

 the opposite way to those of the original shoot. The 

 basal part of the cells is slender for some distance 

 before the expansion commences ; and the germina- 

 tion of a new cell is a slender tubular process ; and 

 this, in the case of the commencement of a branch, 

 is the explanation of '' the spinous process beneath 

 the rim," which is mentioned in the specific character 

 by Ellis as if it were an essential part of the cell, 

 which it is not. The name chelata (clawed), if 

 derived, as I presume, from this supposed spine, is 

 therefore a misnomer. 



The cells are pellucid white, but when viewed by 

 transmitted light are tinged of a yellowish horn 

 colour. They are, however, perfectly transparent, 

 especially the upper ones, for those nearest the b«.se 

 are more horny, and are liable to become studded 

 with parasitic Diatomacece. 



The aperture of the cell is large, oval, oblique, and 

 surrounded by a rather high rim. This is covered 

 with an elastic membrane, which, when the polype is 

 withdrawn into its cell, projects considerably beyond 

 the rim (as seen in Fig. 3, Plate VL), but, when the 

 animal is projected to its utmost (as in Fig. 4), 

 shrinks within the homy rim and becomes concave. 



N 



