BEARERS OF THE HEREDITARY QUALITIES 59 



as regards the number of their chromosomes. On the other 

 hand, the cytoplasm of the relatively large, passive, often food- 

 laden and ensheathed ripe ovum is typically as different as 

 possible from that of the very minute, actively mobile, usually 

 short-lived spermatozoon. The constancy and frequent com- 

 plexity of the reduction-processes which secure the equivalence 

 of chromosomes suggest that these bodies are of paramount 

 importance in inheritance. 



Fig. 14. — The chromatin elements of the nuclei in coil (a), double star (6), 

 and almost divided stages (c). (After Pfitzner.) 



3. Argument from fertilisation. — In typical cases of fertilisa- 

 tion in animals, and in many plants as well, a spermatozoon 

 enters an ovum, sometimes a hundred thousand times larger 

 than itself. As it enters it may leave behind it the locomotor 

 " tail," which has discharged its function, thus further reducing 

 its infinitely small stock of cytoplasmic material. The " head " 

 of the spermatozoon, which is mostly nucleus, and the little 

 " middle piece " which carries the centrosome, are apparently 



