LECTURE XVI. 445 



isms whicli occupy an intermediate position between the 

 vegetable and animal wo:4d^ and thus apparently constitute a 

 connecting link between tbe two kingdoms, we must, on the 

 other hand, not forget that " cell" is only an abstract notion, and 

 that there prevail many diversities in the individual cells of 

 the various organisms and their respective organs — differences 

 which must be considered as original, and which therefore 

 from the very beginning impart to the organisms arising from 

 them a special direction in development. If, therefore, it be 

 said that all organisms arise from a single cell, and that this 

 cell is the fundamental and primordial form of the organism, 

 it is perfectly correct ; but if it be attempted to reduce all 

 existing organisms to one primordial elementary cell, from 

 which they may have been developed, the axiom is false. Not 

 only do organisms that stand in an intermediate position 

 between animals and plants consist of different kinds of cells ; 

 not only are these cells developed in a different mode, so that 

 we are able to distinguish different species of these organisms ; 

 but also those egg-cells from which the more compound organ- 

 isms are developed, show, from the beginning, a fundamental 

 difference both in form and subsequent development. The 

 attempts, therefore, to reduce the whole organic world to one 

 fundamental form, so to speak, to one primordial cell, from 

 which all organisms have been developed in different directions, 

 are as futile as the assumption of those naturalists who con- 

 sider that the whole organic creation had been developed 

 from an elementary plastic matter, the so-called primordial 

 slime. In assuming the possibility that by the co-opera- 

 tion of some forces — as yet unknown to us — an organic cell 

 may be produced from chemical elements, it is clear that the 

 slightest change in the action of these elements must effect a 

 change in the product, that is to say in the cells produced. 

 But as it is impossible to assume that on the whole surface of 

 the earth the same causes have acted, and are still acting, 

 under the same conditions and with the same intensity in the 

 production of such elementg,ry cells, the deduction is clear, 

 namely, that the original cells from which the organisms were 

 ■ developed must have possessed diversified forms and a different 



