304 Sir as burger . — The Periodic Reduction of 
as in animals, that all possibility of misinterpretation is 
excluded, and that their importance cannot be overlooked 1 . 
Just as the facts ascertained among plants exclude the 
assumption of nuclear division with reduction, so also do the 
observations on nuclear division in plants give no support to 
the view that karyokinesis is ever attended with hereditarily 
unequal division, and, so far as my information goes, the 
observations made on animals are likewise unfavourable to 
this vieWo Ever since an accurate knowledge of the longi- 
tudinal splitting of the chromosomes during nuclear division, 
and of the equal distribution of the products of this splitting, 
was attained, I have become more and more firmly convinced 
that the object of the process is the qualitatively equal 
division of the chromosomes. Theoretical speculation, which 
transcends the limits of experience, must start from definitely 
ascertained facts. Minute investigation of the longitudinal 
splitting of the chromosomes can but produce the impression 
of equal division : there is absolutely no foundation in fact 
for the assumption of unequal division. Hence, from the 
very beginning, I have taken the standpoint of epigenesis in 
forming my theoretical interpretation of the facts of develop- 
ment 2 . The only conception of development that I am able 
to form is that it is a succession of stages, such that each 
stage determines the conditions for the succeeding stage and 
inevitably leads on to it. In my opinion, development 
belongs to the category of correlative processes, and can only 
be comprehended from this point of view. The cell-nuclei, 
in whatever part of the body they may be, are and remain 
1 See Boveri, Zellen-Studien, Heft I, 1887, p. 13 ff., 77, and Heft III, 1890, p. 51 : 
also August Brauer, Ueb. das Ei von Branchippus Grubii von der Bildung bis zur 
Ablage, in Anhang zu den Arbeiten der Akad. d. Wiss. zu Berlin, 1892 : 
O. Hertwig also admits the possibility of the reference of division with reduction 
to normal nuclear division in his Ei- und Samenbildung bei den Nematoden, 
Arch. f. mikr. Anat., Bd. 36, 1890, pp. 65 ff. of the separate copy. 
Also Valentin Iiaecker, Ueb. Generation und Embryosack-Mitosen, &c., 
Arch. f. mikr. Anat., Bd. 43, 1894, p. 759 : see also my work, Schwarmsporen, 
Gameten, &c., p. 151. 
2 See, Das Protoplasma und die Reizbarkeit, 1891, pp. 20, 27. 
