186 Prof. H. Karsten on the Formation, 



of the fission-theory account not only for the nested membranes 

 occurring in every individual cell, but even for the general cel- 

 lular envelope of the entire organism (cuticle), and also for the 

 intercellular substance, at least as far as the existence of the 

 latter is admitted by them. 



According to this theory, the outer thickening layer of the 

 primitive, freely produced cell, which forms the basis of the deve- 

 loping organism, must be the commencement of the enveloping 

 membrane ; it is produced whilst the cell, constantly increasing 

 in volume, has its space repeatedly divided into smaller com- 

 partments by fold-formation of its inner layer (the primordial 

 sac). 



Each of the cells thus produced is supposed to secrete the 

 connective mass (intercellular substance) which unites them 

 into a coherent tissue, just as the various layers of which the 

 cell-wall consists are secreted externally and internally by the 

 primordial sac. 



On the other hand, those histologists who believe that cells 

 do not originate by constriction, but as independent structures 

 within the fluid contents of the mother cell, and who are con- 

 vinced that, along with the production of laminse by the assimi- 

 lative faculty of the cell-wall, there is also a simultaneous che- 

 mical change, and in many cases a remarkable regeneration of 

 the mother cell by the endogenous development of daughter 

 cells — such observers dissent from the previous views regarding 

 the origin of intercellular substance only so far as to assume 

 that the growth of laminae does not arise from an excretion of 

 the original cell-membrane (the primordial sac), but by intus- 

 susception into its mass. They also conceive that the inter- 

 cellular substance, which is doubtless present in the interspaces 

 of the active cells, was at one time the outermost cell-membrane 

 or layer of a cell-membrane, but that this has become changed 

 by the agency of assimilation in such a manner that it is sub- 

 jected to the solvent power of the nutritive fluid which soaks 

 the vegetable tissue and becomes received into its mass. 



The explanation of the origin of the membranous envelope 

 (cuticle) as an excretion of the epidermis does not harmonize 

 with the visible peculiarities of this lamina as pointed out by 

 Brongniart, who describes it as a delicate homogeneous covering 

 of the epidermis j for should the laminse of the cell-wall, toge- 

 ther with the cuticle, arise simply by excretion from the cells, 

 the homogeneous nature of this membranous investment would 

 be destroyed by the first act of division of the germ-cell, as it 

 would then be secreted first by two and soon afterwards by four 

 or many cells, and finally by the epidermic layer. In accordance 

 with this mode of origin, it would rather have presented a struc- 



