THE FER T I LIZA T ION-RE AC TION 



assumes great significance for the understanding of the 

 process, fertilization. Moreover, as we shall see, in this 

 study inheres another value, since these happenings are of 

 prospective significance for the whole range of consecutive 

 form-changes by which from the e^^ the animal emerges, 

 changes which taken together we speak of as the egg's 

 development. 



The evidence summarized in the preceding chap- 

 ter makes it clear that in fertilization it is the egg-cyto- 

 plasm that reacts with the spermatozoon. A recital 

 of this evidence is here unnecessary; one fact noted we 

 may recall. This is that whilst no animal sperm-cell 

 is capable of fertilizing an egg except as a spermatozoon — ■ 

 a sperm-cell which has completed both maturations and 

 has become transformed from a spermatid into a spermato- 

 zoon by nuclear condensation and remarkable cytoplasmic 

 changes — the egg, depending upon the species, has capacity 

 for fertilization before, during or after maturation. Thus 

 the fertilizability of all animal eggs hangs together with 

 some condition in the cytoplasm of the egg and is independ- 

 ent of its nuclear state, as germinal vesicle, as first or second 

 maturation-nucleus or as a completely matured nucleus. 

 This fact would still stand were the events in the ensuing 

 fertilization-process the same in all eggs; it becomes of 

 paramount significance since we can not reduce these events 

 to a common underlying principle which holds for all 

 eggs. 



Some change, then, supervenes in the egg-cytoplasm 

 which transforms it from a condition of non-fertilizability 

 into one of fertilizability. Since we intend to examine the 

 reaction between egg and spermatozoon at the moment of 

 insemination, and since we know that spermatozoa are at 

 this time alike with respect to fertilizing capacity, our 

 task concerns itself with the fertilizable condition of the 

 egg-cvtoplasm. 



185 



