216 GENERAL EMBRYOLOGY 



would follow from this that the two germ cells are of more 

 nearly equal importance in the process of heredity. 



We may finally conclude from all of the foregoing discussion 

 that little can be very definitely asserted regarding the real 

 function of fertilization now, and still less regarding the 

 original significance of the process. Some of the questions 

 involved here are to-day the most interesting and important of 

 the unsolved problems in the fields of Embryology and Biology. 



It is reasonably clear that fertilization is not, at the present 

 time, a simple process, although it may have been so originally. 

 Doubtless there has been an evolution both of the process and 

 of the consequences of fertilization, just as there has been of all 

 organ structure and organ physiology. Furthermore, it 

 seems clear that the various possibilities described above, as to 

 the significance of fertilization are not mutually exclusive: 

 fertilization may be important for several of these reasons, even 

 in a single case, and probably it has no one meaning that is 

 exclusively true. It is quite possible that normally, among 

 the Metazoa to-day, the spermatozoon may bring about in the 

 ovum the formation of centrosomes which do, as a matter of 

 fact, take an important part in the succeeding cleavages of 

 the zygote, it may also chemically and physically stimulate 

 the ovum to develop by bringing about initial changes in its 

 chemical or physical structure or organization, it may at the 

 same time introduce substances, the effect of which is " rejuve- 

 nation " of the specific protoplasm apart from the reproductive 

 phenomena, and finally the structure of the spermatozoon which 

 does these things may also affect the course of development so 

 that individual characteristics of the male parent, as well as 

 of the female parent, may appear. And to say that the result 

 of fertilization is, for example, rejuvenation, need not mean 

 that it is not also a stimulus to reproduction, a controlling factor 

 in variation, and a means of heredity. 



REFERENCES TO LITERATURE 



ADOLPHI, H., Ueber das Verhalten von Wirbeltierspermatozoen in 



stromenden Fliissigkeiten. Anat. Anz. 28. 1906. 

 VAN BENEDEN, E., (Ref. in Ch. II.) 



