GENERATION AND INHERITANCE 295 



known saying, "omne vivum ex ovo." But when Leeuwenhoek, dur- 

 ing his microscopic discoveries, found the spermatozoa, the thought 

 occurred to him that the worm-like bodies in the semen which moved 

 independently, and thereby showed a certain resemblance to the low- 

 est organisms, should be more properly considered as the miniature 

 beings. He, therefore, proposed the hypothesis that the spermatozoa 

 penetrated into the egg during fertilization in order that the latter 

 might serve them as a suitable nourishment for their future growth. 

 No less a person than Leibnitz accepted this hypothesis. 



Strangely enough, in both hypotheses, which appear to be ex- 

 cluded together with the dogma of preformation, a seed of truth 

 seems to be hidden. For, as is easily seen from our present stand- 

 point, both egg and sperm take an equal part in the formation of the 

 new being. Both are cells, one of which represents the properties of 

 the female, the other the properties of the male progenitors. Both 

 unite to produce a mixed product, which has inherited the peculiar- 

 ities of both parents. 



Here we see again how the development of scientific views in the 

 realm of embryology is dependent upon the contemporary develop- 

 ment of all science. We can appreciate the fact that the old scien- 

 tists could not understand the process of generation, because at that 

 time the lack of microscopic assistance hid from them the concep- 

 tion of the elementary construction of the organisms. 



The thought of the union of two organisms into a new unit could 

 not occur to the adherents of the preformation theory, for if embryos 

 are already miniature beings composed of many organs, how could it 

 be possible that they should unite in pairs to form a single individual, 

 and at the same time their organs and tissues flow together into one? 



For us who know that the germs are merely cells separated from 

 their parents, thus similar to simple elementary organisms, the con- 

 ception of an amphimixis has no such difficulty, and for us it is now 

 a determined fact. We can follow under the microscope the union of 

 a male and a female cell and even the union of their component parts, 

 especially their nuclei and the substances contained therein. With 

 the knowledge of amphimixis the phenomenon that children may 

 resemble both their parents, a fact for which scientists until the 

 nineteenth century could give no logical explanation, is brought 

 within our understanding. They resemble both, because they are 

 formed from a union of the substance of the father and mother; in 

 other words, from a paternal and a maternal element. 



At this point the problem of generation and fertilization passes 

 over into the most difficult of all problems, the problem of inheritance. 

 However, before we approach this more closely, it will be well to 

 make ourselves familiar with the series of phenomena which stand 

 in the closest relation to the problems of generation and inheritance 



