THE FERriLIZATION-PROCESS 



organisms from which the eggs and spermatozoa come. 

 In this bringing together of the haploid chromosome- 

 garniture from the mother and the haploid from the father, 

 fertilization not only insures the constancy of the species' 

 characteristic chromosome-number, but also, since the 

 chromosomes are concerned in heredity, it maintains equi- 

 librium between paternal and maternal inheritance as far 

 as this is determined by the chromosomes. This similarity 

 of nuclear structure in egg and in spermatozoon has thus 

 significance for the development that results from ferti- 

 lization, but as a static, non-changing factor it can not be 

 related to that radical and far-reaching change in the egg 

 that we denominate fertilization. We, therefore, turn to 

 the discussion of the other characteristics of the partners 

 and shall find in them many differences. 



Animal spermatozoa exhibit great diversity in structure. 

 In general, they may be classified as flagellated and non- 

 flagellated. The larger number of species of animals have 

 spermatozoa of the former class. Typically one such sper- 

 matozoon is made up of a head (the nucleus) which may be 

 spherical, bullet- or lance-shaped, to whose anterior end 

 generally is fitted a cytoplasmic cap, the so-called per- 

 foratorium, which may be very blunt, as in the starfish- 

 spermatozoon, or more spike-like as in the Nereis- or the 

 Cerebratuhu-speiTaatozoon. The cytoplasm located behind 

 the head is called the middle-piece; it varies greatly but 

 often contains one or more granules of a lipoid nature. 

 The tail or flagellum, the third cytoplasmic structure, is 

 continuous with the cytoplasmic film enclosing the sperm- 

 head and may be of very great length; it is the locomotor 

 appendage of the spermatozoon. 



Non-flagellated spermatozoa may have the form of a 

 truncated cone. Or they are more definitely amoeboid in 

 form, as in crustacean spermatozoa such as the lobster's, 

 crab's, etc. That is, instead of the blunt contracted form 



