268 THE EVOLUTION THEORY 



as the essential elements of the spermatic fluid. When one follows the 

 matter out in detail, one finds it almost incredible tha.t such a number 

 of mistakes should have been made, and so many circuitous paths 

 traversed, before even the limited knowledge current in the middle 

 of the nineteenth century was attained — that is to say, enough to give 

 ground for the assertion that fertilization depends upon the contact of 

 the spermatozoon with the body of the egg. In 1843 Martin Barry 

 had found the spermatozoa within the egg-envelope of the rabbit ovum, 

 but it was some time later (1853) that the investigations of Meissner, 

 BischofF, and Newport established the fact that the zoosperm penetrates 

 through the egg-envelope. All else remained quite obscure, and could 

 not be cleared up as long as it was believed, on the strength of 

 observations which were in themselves correct enough, that several 

 zoosperms were always necessary to fertilize one ovum. 



To an understanding of the process even in its most general outlines 

 there was lacking, apart from technical methods, an appreciation of 

 the morphological value of the ovum and the spermatozoon. It was 

 necessary to recognize both ovum and spermatozoon as cells before 

 their union in fertilization could be regarded as the fusion of two 

 cells, as a copulation or conjugation of two minute elementary 

 organisms. But this knowledge only gained ground very gradually, 

 and even in the sixties opinions on the subject were very much 

 divided. Moreover, there was an entire absence of knowledge in 

 regard to ' sexual ' reproduction among the lower plants, the Algse, 

 Fungi, Mosses, and Ferns, as well as of any detailed acquaintance with 

 the processes of fertilization among flowering plants. All this had to 

 be elucidated by the labours of many distinguished observers before 

 it was possible to say so much even as this, that the process of 

 fertilization depends in generial on the union of two cells. 



I need not discuss the whole of this long process of scientific 

 development, and have only touched upon it because I wished to 

 emphasize that the conception of the process of fertilization was for 

 a long time quite erroneous, and has only attained to clearness in 

 recent times. Pairing as it is seen in the higher animals was for long 

 regarded as the essential part of the process, and a mysterious life- 

 awakening influence was assumed in regard to it ; and even when it was 

 understood that not the copulation, but the union of two living units 

 which was always brought about thereby — the union of the male and 

 the female germ-cells— was the essence of ' fertilization,' this was still 

 regarded as a life-awakening process, and the way to a true under- 

 standing of the facts was thus once more blocked. 



The simplest form of sexual reproduction in many-celled animals 



