Algal Genera Acicularia and Acetabulum 325 



calcareous incrustation ; and every spore seems to have a surface 

 exposure. When the massula, viewed from above, appears un- 

 usually broad, it can be shown to be hollow toward the larger 

 end. In most cases, however, it is solid, except for the small 

 interstices, and toward the larger extremity is concave at the sides 

 (Figs. 37 and 38), so that a vertical transverse section has some- 

 what the form of a biconcave lens. This arrangement, whereby 

 each aplanospore has its lid-bearing surface exposed and uncal- 

 cified, is an interesting adaptive feature which seems to have escaped 

 formal recognition hitherto. Count Solms-Laubach in figuring * a 

 portion of the surface of a massula does not fail to indicate that 

 the lids of some of the spores are visible, but in describing the 

 11 lime-spicula " (our massula) he writes f as follows : u It consists 

 of a strongly calcified substance enclosing numerous cavities lying 

 near the surface, and consequently transparent. In each of these 

 and completely filling it there is a spore of the same structure as 

 those of Acctabularia. It follows that the pits of the fossil forms 

 are the spore-containing cavities from which the spores have dis- 

 appeared and the external lime-covering has not been preserved, 

 so that they appear as opening outwards. " 



In the Bermudian specimens, and in the Brazilian so far as we 

 have seen them, the spore-cavities not only lie w near " the surface 

 but actually reach the surface and for a region approximately cor- 

 responding to the spore-lid there is no "external lime-covering " 

 to disappear; and the cavities not only "appear as opening out- 

 wards/' but such is actually the case from the beginning. This is 

 shown in an especially striking fashion when massulae from for- 

 malin-preserved material are allowed to dry on a glass slide and 

 are observed under comparatively low magnification with reflected 

 light. The spores in shrinking away from the surface leave actual 

 openings. It can be determined more accurately by use of high 

 powers and transmitted light that the lid is either wholly free from 

 the calcareous coating or is at most but partially covered with an 

 unimportant amount of it. 



By transmitted light, the matrix is yellowish, minutely granu- 

 lar, and somewhat waxy in appearance. As has already been 



t /"• C. IO. 



