CHAPTER VI 

 THE PROBLEM OF SPECIFICITY IN FERTILIZATION 



In fertilization we have both tissue and species 

 specificity. The spermatozoon does not react with, 

 nor penetrate, other kinds of cells than the ovum 

 (tissue specificity), a fact that suggests the question 

 whether this is due to a chemical specificity of the egg 

 or merely to its physical characteristics. Fertilization 

 is also species specific, but only in a restricted sense, 

 because it is possible to a certain extent between dif- 

 ferent species or even wider groups (hybridization); 

 the degree of this specificity is subject to rather wide 

 variations in different animal groups, but it is in a 

 very general sense defined by taxonomic relations. 

 Within the species also there are undoubtedly individ- 

 ual variations in fertility, which reach an extreme in 

 the phenomenon of self -sterility in certain ascidians. 



I. TISSUE SPECIFICITY 



Kohlbrugge (1910, 191 1, 191 2) maintains that sper- 

 matozoa freely penetrate the epithelial cells of the 

 uterine mucosa in animals with internal fertilization 

 that he has studied (bat, mouse, rabbit, hen, dogfish, 

 skate) and may even pass through these into the under- 

 lying connective tissue. Sobotta (191 1) was unable to 

 confirm the observations (on the mouse) and showed 

 that most of the spermatozoa degenerate without free- 

 ing themselves from the ejaculate. He criticizes Kohl- 

 brugge severely for his methods, and suggests that the 



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