THE BIOLOGY OF THE CELL SURFACE 



reaction; besides, there is no evidence that the sperma- 

 tozoon initiates fertilization by means of an enzyme, 

 though enzyme-reactions certainly follow after fertilization. 



As I see it, specificity in fertilization depends in part 

 upon the chemical constitution of the blood or body-fluid 

 of the species which produces the eggs and spermatozoa. 

 Whilst the chemical constitution of the egg of a species 

 differs from that of all other cells comprising the animal's 

 body, nevertheless there is a chemical similarity among all 

 cells of the animal's body including the Q^g^ inasmuch as 

 they are all nourished by the same body-fluid. Species- 

 spermatozoa have the identical chemical structure as eggs 

 to the extent that they are products of the same species' 

 body and blood; at the same time they differ chemically in 

 other respects from eggs. Blood (or body fluid) is different 

 from all cells including eggs and spermatozoa. Now where 

 blood inhibits species-fertilization, this inhibition is owing 

 to its being present in such amount that it makes inert 

 the specific substance in the egg's ectoplasm. A smaller 

 amount blocks foreign spermatozoa and this amount can 

 not be wholly removed except by injury of the ectoplasm. 

 In nature, owing to the breeding habits of animals, eggs 

 and spermatozoa of one species tend to be emitted simul- 

 taneously within a fairly restricted breeding ground. Thus 

 the chances for specific fertilization are enhanced. Where 

 copulation takes place, specific fertilization is still more 

 highly insured. On the other side, laboratory conditions 

 for inducing cross-fertilization could scarcely obtain in the 

 open sea. If nevertheless cross-fertilization should happen 

 in nature, we can relate it to an injured state of the egg's 

 ectoplasm. i 



As stated above, spermatozoa do not enter such fertilized 

 eggs, or fragments thereof, which are normally mono- 

 spermic, i.e., into which only a single spermatozoon enters. 

 The prevailing opinion concerning the block to poly-sperm- 



igS 



