448 Sargant . — The Formation of the 
structure, and all the twenty-four chromosomes of the latest 
archesporial division are represented in the sexual nucleus. 
But Dr. Haecker predicts on the faith of zoological analogies 
that one of the three oogenetic nuclear divisions with twelve 
chromatic segments and one of the four similar spermato- 
genetic divisions will be found to result in the division of each 
segment not longitudinally but transversely, and in such a way 
that each half represents one of the original twenty-four 
chromosomes. If this should prove true, the descendants 
of the original twenty-four chromosomes would be divided 
during this karyokinesis between the daughter nuclei, twelve 
going to one and twelve to the other. This would be a true 
reduction division in Professor Weismann’s sense. The 
sexual nucleus thus formed would be constructed of the 
descendants of twelve only from among the original twenty- 
four chromosomes. 
It is clear that Dr. Haecker’s hypothesis rests on three 
assumptions. 
1. That the reduction in number of the chromosomes which 
has just been described is caused by the joining of twenty- 
four chromosomes from the previous nuclear division end-to- 
end in twelve pairs. 
2. That in a subsequent nuclear division, before the 
formation of the ovum on the one hand or of the male 
generative nucleus on the other, the twelve double seg- 
ments thus formed are divided not longitudinally but 
transversely. 
3. That this transverse fission corresponds to the junc- 
tion formerly accomplished between the members of each 
pair. 
Assumptions 1 and 3 are not in themselves improbable, 
but in order to verify them it would be necessary to identify 
each chromosome from one karyokinesis to another through- 
out the intervening resting-stage. This has not hitherto been 
found possible. The second assumption can be proved or 
disproved by observation. For in so favourable a case as 
the anther or embryo-sac of L ilium Martagon it is very 
