240 THE PHENOMENON OF 



proportion to their frequently very considerable size, 

 a large internal cavity filled with watery fluid, parietal 

 distribution of the consistent portion of the contents, 

 fully-developed starch-grains, &c. To such old-born cells 

 belongs the gradually advancing multiplying division, as 

 has. been described by Mohl. 



1. Reconstruction with division into two daughter- 

 cells, in the do^nain of vegetative cell-formation. 



a. Halving through evidently gradual constriction ; 

 Old-cell-division. — The primordial utricles of the daughter- 

 cells are cut off by a process of formation advancing 

 gradually from the periphery to the centre ; the formation 

 of the cell-membrane commences before the conclusion of 

 this cutting off, the septum is consequently formed in the 

 shape of an annular ridge (or properly a double-plate) 

 gradually increasing in breadth, finally closing-in in the 

 centre. 



a. Without a nucleus? Here refers the cell-division 

 of Cladophorce, in which at least no nucleus has yet been 

 found. It has been described in detail by H. von Mohl,* 

 in Cladophora glomerata, as above mentioned. 



/3. fFith a nucleus. — My observations on this point, 

 to be brought forward here, were made on Spiroggra 

 nitida and jugalis, which are probably both forms of one 

 and the same species, the former „ — jg, the latter about 

 5 millini. in diameter. The position and character of 

 the nucleus of Spiroggra are well known; it appears 

 particularly sharply and distinctly when spirit is applied, 

 which however generally disturbs its originally central 



* 'Vermischte Schriften,' p. 362, t. xiii. With regard to the mauy- 

 layered membrane marked b in fig. 5, and c in fig. 14, T venture to remark 

 that the same is wrongly described at page 365, as a connected tubular 

 envelope of all the cells, as it were a colossal branched cell. Only the 

 gelatinous, slimy investment marked a, (fig. 5,) and d, (fig. 14,) forms such 

 an universal envelope ; the many-layered membrane, on the contrary, forms 

 a very complicated system of encasement, since its innermost layer encloses 

 only two cells, its inmost one but three cells, and so on outward a pro- 

 gressively larger number of cells. In the further description, indeed, 

 especially at pp. 368-69, the assertion made at first is partially corrected 

 by Mold himself. 



