CHANGES IN REPRODUCTIVE CELLS OF ELASMOBRANCHS, 299 
demonstration in fact. Unfortunately, however, for the Re- 
ductionstheilung, as well as for the enormous superstructure 
which Weismann has lately piled upon it, O. Hertwig’s obser- 
vations have been shown by Brauer to be quite erroneous, 
there being in the spermatogenesis of this animal no such 
thing as a division in which alternate chromosomes pass 
unsplit to daughter-cells. So also, during the Elasmobranch 
spermatogenesis with which we have been dealing (the 
course of which will be found summarised in these pages at 
the end of each spermatogenetic period), there is nothing com- 
parable with the ‘‘ Reductionstheilung ” of Hertwig, which is 
made such an integral part of Weismann’s last theory of 
heredity. It is true that there is a numerical halving of the 
chromosomes, between the first and second spermatogenetic 
periods, but this is brought about in the synapsis which 
separates the one period from the other, and has nothing to do 
with division at all. 
It is so necessary to be quite clear about this, that I have 
subpended a few lines of Weismann’s treatise in which his 
conceptions of the ‘‘ Reductionstheilung ” are given in full. 
On page 11 of the English translation of the ‘Germplasm,’ 
its author, after speaking of the necessity of a “ Reductions- 
theilung,” and as though the universality of its occurrence was 
an established fact, goes on to say :—“ The hypothesis of the 
Reductionstheilung has been thoroughly substantiated by sub- 
sequent observations—in fact, it has even been proved that in 
many cases this reduction occurs exactly as I had foretold and 
represented in a diagrammatic figure; that is to say, by the 
non-occurrence of the longitudinal division of the chromo- 
somes, which occurs in ordinary nuclear division, and by the 
distribution of these in the daughter-nuclei. This holds good 
for the ovum as well as for the sperm-cell in animals, and as 
far as is known,in plants also. The germ-cell must in 
all cases by division get rid of half its nuclear rods.” Again on 
page 236 :—‘‘ We now know that this reduction in the number 
of the ids, by one half,is of general occurrence, and is effected 
by means of the nuclear divisions which accompany cell divi- 
