EEPRODUCTION AND HEKEDITY 291 



run away, unless he wants to serve as a meal for the ravenous 

 female. 



Among the cuttle-fishes, too, fertilization takes place by means 

 of spermatophores. These have such' a remarkable structure and, 

 owing to the swelling, perform in the water such strange move- 

 ments that they have been described as independent parasitic 

 worms. The transference of the spermatophores to the other 

 sex is performed by the ' hectocotylus,' one of the tentacles of the 

 male which has been specially transformed for this purpose. In 

 Argonauta this hectocotylus separates during copulation and 

 enters the mantle-cavity of the female where it continues to live 

 for some time. It was therefore formerly looked upon as the 

 rudimentary male of the Cephalopods. 



In dealing with the interesting processes which take place 

 during the maturing of the sex-cells and their preparation for the 

 copulative act and copulation itself, we must recall what we have 

 heard about indirect nucleus-division or mitosis. We saw that 

 each individual body-cell of a certain animal-species always 

 contains the same number of chromosomes. All cells, for 

 instance, of Ascaris megalocephala bivalens, have only four chromo- 

 somes, all human body-cells sixteen. This normal number is 

 maintained in all descendants by the dividing mechanism which 

 works with mathematical precision. It will be remembered that 

 the chromosomes were regularly doubled before cell-division by 

 longitudinal fission, and that each of the two young daughter- 

 cells received half, that is, once more the normal number of 

 chromosomes. These behave in their reproduction almost like 

 independent organisms which reproduce by division. 



The act of fertilization consists in the fusion of a male with 

 a female sex-cell. As the ovum as well as the spermatozoon are 

 typical complete cells, we should nearly expect the fertilized 

 ovum to contain double the normal number of chromosomes. But 

 if that were so, the animal originating from the fertilized egg by 

 cell- division would, in its turn, have twice as many chromosomes 

 in each body-cell as its progenitors. The act of copulation 

 would therefore plainly lead to an accumulation of the chromatic 

 elements which would be doubled in each succeeding generation. 

 But that must not be and is, indeed, contrary to all observations. 

 The cell-nuclei of sexually-begotten children and grandchildren 

 have always exactly as many chromosomes as the nuclei of their 



