450 MOSSES AND FERNS chap. 



but this does not occur until a comparatively late stage. The 

 nucleus is here somewhat flattened to begin with, and the coils 

 of the spermatozoid lie nearly in the same plane and resemble 

 a good deal those of Marattia, except that they are larger. The- 

 protoplasm enclosed within the coils is conspicuously granular, 

 and forms the large vesicle attached to the posterior coils of the 

 free spermatozoid. The mucilaginous change in the walls of 

 the sperm cells begins about the same time as the differentiation 

 of the spermatozoids. 



The free spermatozoids consist of from two to three com- 

 plete coils, of which the forward one or two are very much 

 smaller than the very large and broad hinder one, which encloses 

 the vesicle. The cilia are much like those of the Fern sperma- 

 tozoid, but somewhat shorter. The cover cells of the ripe an- 

 theridium are forced apart by the swelling of the mucilage from 

 the disorganised walls of the sperm cells, which are forced out 

 of the opening into the water, where the remaining wall of the 

 sperm cell is dissolved and the spermatozoid set free. When 

 in motion a peculiar undulation of the large posterior coil is 

 conspicuous, a phenomenon which has also been observed in the 

 quite similar spermatozoids of Osmunda. 



The young female prothallium is always a cylindrical mass 

 of cells with a series of thin lateral lobes. After the archegonia 

 begin to form and a definite apical meristem is established, the 

 formation of these lobes is almost exactly like the similar ones 

 in young plants of Anthoceros fusiformis. The exact relation 

 of the growing point in the older prothallium to the primary 

 one could not be made out. In the former this arises, according 

 to Buchtien ( i ) , upon the under side of the prothallium, with- 

 out any apparent relation to the primary growing point. This 

 much is certain, that just before the first archegonium appears, 

 there is formed a cushion not unlike that of the Ferns. In the 

 youngest condition this in profile (Fig. 262, A) shows an evi- 

 dent apical cell (probably one of several), not unlike that of the 

 Ferns; but the great difficulty of obtaining accurate sections 

 through it made it impossible to follow exactly its further de- 

 velopment. This much can be stated confidently, however, 

 that at the time when the first archegonia are produced, the 

 structure of the prothallium is essentially that of Osmunda 

 or Marattia, and consists of a central massive midrib and a 

 one-celled lamina, which is not continuous, but composed of 



