246 THE PHENOMENON OF 



and is about half as thick as the second, &c. By the 

 increased expansion and corresponding attenuation, which 

 the cell -membranes of the mother-cells lying further back 

 in the series of generations undergo, it is conceivable 

 that they must become constantly less clearly distinguish- 

 able as separate layers, and finally vanish entirely. Each 

 such layer, or rather special cell-membrane, is itself again 

 composed of numerous extremely delicate lamellse, formed 

 successively during the life-time of the individual cell, 

 which, however, can only be detected in the inner thicker 

 layers, and there very indistinctly. The character of the 

 septa is most intimately connected with this system of 

 encasing of the cell-membranes. Between two sister-cells 

 the septum is composed of the mere continuation of the 

 innermost cell-membrane (that belonging to the individual 

 cell), clearly passing over into this, and increasing in 

 thickness in equal proportion during the growth of the 

 cell. The structure, as composed of two lamellae, may 

 be detected even in the very thin septa of young sister- 

 cells, in the swoUen-up condition. No intercellular 

 passage exists at first in the periphery of the septum, but 

 it is gradually formed during the increase of thickness of 

 the septum, and is situated between the membrane of the 

 mother-cell and the two daughter-cell membranes forminc 

 the septum. The septum between two pairs of daughter- 

 cells (between the first-cousin-cells), is formed of the 

 membranes of the daughter-cells and those of the mother- 

 cells, thus of four laminae; the intercellular passage 

 existing at its periphery is situated between membrane 

 ofthe grandmother-cell and membrane of the two adjacent 

 mother-cells. The septum between two double pairs of 

 of first-cousin-cells (between second-cousin-cells), is 

 formed of the membranes of the daughter-cells, mother- 

 cells, and grandmother-cells, thus of six layers; the 

 intercellular passage lies between the adjacent grand- 

 mother-cell membranes and the membrane of the great- 

 grandmother-cells, which, however, (together with all the 

 membranes lying outside it,) is so thin, that it appears as 



