138 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



the mother-cells of the first and second order, and the germ- 

 cells. The series A represents eight ids in each of the 

 two idants of a primitive germ-cell, arranged as a single 

 row; whereas in series B they form two rows. In A the 

 idants of stage / give rise, by longitudinal fission, to the four 

 idants of stage //, that is to two pairs of identical idants : in series 

 B the two original idants similarly produce the four idants 

 of stage //, each of which is different from the others and 

 contains only four ids. In consequence of this, in series B, the 

 two successive * reducing divisions ' diminish the total number 

 of ids in the cell, first (stage ///) from 16 to 8, and then 

 (stage IV) from 8 to 4 — i. e. to one quarter the normal number 

 of ids ; in series A, on the other hand, the corresponding 

 divisions lead to ^hat halving of the normal number of ids 

 which is in accordance with theory — i. e. from the 16 of stage / 

 to the 8 of stage IV. 



It should be regarded as certain that many identical ancestral 

 units may be present in the germ-plasm of a germ-cell, and that 

 identical nuclear rods may exist side by side. Furthermore, 

 during fertilization, as has been mentioned above, identical 

 nuclear rods from the two parents must meet together, the 

 frequency of this depending upon the amount of interbreeding 

 (using the term in its widest sense) that has occurred, or in 

 other words upon the limit set to the number of individuals in 

 any given area, and upon the restriction in the number of 

 ancestors of the species. Such considerations enable us to 

 understand why nature has provided such superabundant 

 variations in the germ-plasm of the reproductive cells of a 

 single individual. It is the same with the more obvious prodi- 

 gality that she lavishes in the millions of germ-cells brought 

 forth by every iudWidudilAscaris or sturgeon. We now know that 

 this apparent waste is necessary in order to ensure that, on the 

 average, at least one or two germs may reach maturity, and 

 that thus the species may be maintained. 



Other Types of Maturation of Germ-Cells. 



I would here repeat that, before O. Hertwig, Platner had 

 shown that an entirely similar process occurs in the double 

 ' reducing division ' of the mother-cells of the spermatozoon in 

 both the butterfly and the snail. He observed the original 



