UTRICULAR STRUCTURES. 



171 



on account of the minute size, or the opacity of the 

 nucleus. It is, moreover, probable, when at a later 

 period several nucleoli are met with in one nucleus, that 

 one alone existed in the first instance, and that the rest 

 have originated subsequently. I have already expressed 

 my opinion on this point in the section on " Free cell- 

 formation" of the preceding essay.* 



The nuclei terminate their existence either by solution, 

 in consequence of weakness resulting from age, or by 

 propagation. The mode in which nuclei propagate, has 

 already been described when treating of their origin. 



2. Spermatic Utricles. 



The spermatic utricles are those in which the spermatic 

 filaments originate. Hitherto they have been called cells 

 or cellules. I formerly thought that they might have 

 the import of nuclear utricles, because always one such 

 utricle appeared in a cell in the antheridia of the Cha- 

 raceae, and because a nucleolus always existed previously 

 in each utricle. 



Without intending now to deny this analogy, I believe 

 that the spermatic utricles are not perfectly identical with 

 the nuclear utricles ; in the first place, because the pro- 

 duction of the spermatic filament is a characteristic of 

 which the nuclei are wholly devoid, and further, be- 

 cause in animals, and probably also in plants,! several 

 such utricles are sometimes formed in one cell. 



It is no proof of the spermatic utricles being cells, 

 that in the Elorideae, Mosses, and Ferns, they are applied 

 closely together so as to form an apparent tissue ; since 

 it is quite as possible as not, that they are produced in 

 one large cell resembling an embryo-sac, or that the cells 

 in which they are formed become dissolved. 



* Page 107. 



f Nageli on the Propagation of the Ehizocarpeee ; Zeitschr. fur wiss. 

 Botanik, H. 3, p. 188 (184=6). 



