132 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



duality which takes place in the course of generations, and the 

 fact that one and the same individuality is never twice repeated, 

 suggest to my mind an occasional change in the arrangement 

 of ids within the idants — a change which, if it does not occur at 

 every opportunity afforded by reconstruction, will at any rate 

 take place in the course of generations. 



I will not now enter more fully into the foundation of such 

 protracted, and, to a certain extent, secular changes of the idants, 

 but will turn at once to the problem propounded above as to the 

 meaning and significance of the fact, which has been firmly 

 established by the researches of O. Hertwig upon Ascaris, that 

 a double division of nucleus and cell is rendered necessary by 

 that reduction of idioplasmic elements which is required by my 

 theory in both ovum and sperm-cell ; in other words, to explain 

 the fact that the number of idants is doubled before being halved. 



Inasmuch as two primary polar bodies are formed, so far 

 as we know, by all eggs which require fertilization, we may con- 

 clude that the significance of the double division of the sperm- 

 mother-cell of Ascaris megalocephala is typical and far- 

 reaching, rather than merely accessory or secondary. 



If, as I have shown above, the significance of the original 

 increase of the chromatin rods to double their number does 

 not lie in the needs of the growing ovum or spermatozoon, 

 it must be sought for in some other direction. // lies, as 

 I believe, in the attempt to bring about as intimate a mixture as 

 possible of the hereditary units of both father and mother'^. 



If the first object of sexual reproduction is to combine the 

 hereditary tendencies of two individuals, and not in a mere 

 transitory manner (viz. in the single individual proceeding 

 from one act of fertilization), but permanently, because such 

 a combination affects also the germ-cells of each single indi- 

 vidual, and therefore of all succeeding generations,— if this 

 be its object, then we must admit that it is mechanically pos- 

 sible for a combination of paternal and maternal idants to 

 exist side by side in the mature germ-cells of the individual. 

 This is obviously conceded if the ' reducing division ' makes 



^ Histologists may perhaps object that the doubling of the idants 

 simpl}'^ depends upon a postponement of the normal longitudinal fission 

 until the time at which the spindle is formed. This is probably correct, 

 but it only explains the existence of the doubling and not its significance. 



