LECTURE XLIII. 



THE ACTION OF SEXUAL-CELLS UPON ONE ANOTHER. 

 (CONTINUITY OF EMBRYONIC SUBSTANCE.) 



So far as our experience goes it appears that organic life never commences 

 otherwise than by means of small masses of substances separating themselves off 

 from an organism which already exists. These substances however are not fluid 

 in nature— not watery solutions — although saturated with water, they are not 

 crystalline, nor in the ordinary sense of the word soHd. Moreover, it is here, 

 as it appears, never a matter of a simple chemical compound, but always of a 

 mixture of substances; or, to put it shortly, the material concerned is a minute 

 mass of protoplasm, which usually, especially in the case of asexual reproduction, 

 contains in addition certain plastic materials for growth, such as starch or fat. 

 Nay, many spores take away with them from the mother-plant organs of 

 assimilation also. 



We have every reason to believe, moreover, that most of the visible substance 

 in a reproductive cell forms as a matter of fact only materials for growth in the 

 ordinary sense of the word, and' that in addition, there is present a perhaps 

 infinitesimally small quantity of a substance which, though not well understood 

 itself, constitutes so to speak the primum movens by means of which the other 

 substances of the reproductive cell are sooner or later put in motion, and the 

 processes of growth called forth. 



This view of the nature of a reproductive cell obtains a certain degree of 

 probability from the whole of the pecularities of sexual reproduction. The essence 

 of the latter lies in that in the course of the development of a plant (or of an 

 animal) two kinds of cells are produced, each of which is incapable of further 

 development on its own account, but from the union of the materials of which a 

 product results which is capable of development. Only this latter, the fertiUsed 

 oospore (or in some lower Algae and Fungi the so-called zygote or zygospore) 

 is a reproductive cell in the strict sense of the word, since without fertilisation it is 

 not in a position to give rise to a new organism. It is true it appears exceptionally 

 that even a non-fertilised oosphere may be capable of forming an embryo; but 

 the as yet little understood cases of so-called parthenogenesis may turn out to be, 

 as will be shown in the course of these considerations, rather a confirmation of 

 ■what I regard as the essential in fertilisation. 



An oosphere (or in the case of the Algse a swarming gamete) is rendered 



