REJUVENESCENCE IN NATURE. 149 



original length, separates again into a posterior longer, 

 and an anterior shorter, cell ; which latter repeats the 

 same process, and so on. Thus, by a continually repeated 

 division of the apical cell into two unlike cells, is formed 

 a series of cells of a second order, the link-cells of the 

 filament, the first of which is at the same time the root- 

 cell. The filaments of Ulothrix zonata, once formed, grow 

 no more in thickness, but gradually increase in diameter, 

 from the base to the summit, in such a manner that the 

 anterior parts often appear thrice or four times the diameter 

 of the posterior, lying nearer the root.* The root-cell, 

 as well as those next succeeding it, remain unaltered and 

 are infertile; the following link-cells, on the contrary, 

 after they have attained a length about twice their 

 diameter, divide into two equivalent cells, consequently 

 into cells of the second generation of the second order, 

 whereby, since no further elongation takes place, cells are 

 produced of about equal length and breadth. Still farther 

 forward, therefore in the thicker part of the filament, 

 this division is repeated once or twice more, so as to give 

 rise to cells of the third or fourth generation of the second 

 order, the length of which is only i or \ their diameter. 

 Finally, in the cells of the last generation of the second 

 order, the germ-cells are produced by division of the 

 contents alternately in the three directions of space.f 

 The filaments of (Edogonium., in their earlier development, 

 follow the same course as those of Ulothrix zonata, but 

 diifer in the subsequent subordinate division of the 

 original link-cells, since these do not divide into equiva- 

 lent cells, but into unlike cells, forming series of link-cells 

 of the second degree, which is moreover accompanied by 

 a longitudinal extension of the subordinate link-cells. 

 The lowest link-cell, which expands at the base into a 

 discoid, often elongately lobed root-foot, and is always of 



* Hence the great variability in the diameter of the filament, which 

 varies from T oo to T co> or sometimes ino millim. 



f Vide Nageli, 'Algensysteme,' p. 137, t. i, f. 53, 54. 



