112 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



showed the existence of a polar body in the parthenogenetic 

 ova of the Aphidae, and there is now no doubt that polar bodies 

 are formed in most if not in all parthenogenetic eggs. The 

 ' compensation theory ' must therefore be given up, and the 

 question arises as to the theory which can take its place. 



Before the existence of polar bodies in parthenogenetic ova 

 had been completely established, I had endeavoured to find, in 

 opposition to the ' compensation theory,' another meaning in 

 the polar bodies. The history of our earliest knowledge of 

 the processes of nuclear division, by the work of Auerbach, 

 Butschli, Flemming, and others, is well known : the exist- 

 ence of most remarkable and excessively minute arrangements 

 for cell-division were shown to exist in the mysterious ' chro- 

 matin substance ' of the nucleus, the so-called nuclear loops, 

 which are accurately divided in a longitudinal plane, the halves 

 then entering the two daughter nuclei which are being formed. 

 These chromatin rods acquired a new significance when E. van 

 Beneden first showed that they were contained in equal numbers 

 in both the male and female reproductive cells, and that they 

 arrange themselves side by side, to build up the chromatin 

 substance of the embryonic nucleus. Considering this and 

 certain other facts, it became more and more probable that the 

 chromatin rods were the essential factors in fertilization, the sub- 

 stance which was contributed by the parents and fused together 

 in the offspring, and which was therefore, in all probability, the 

 bearer of hereditary tendencies. Strasburger, O. Hertwig, and 

 V. Kolliker also gave expression to this view for which I had 

 contended. We regarded the nuclear loops as that idioplasm 

 which Nageli had been led, by his acute reasoning, to suggest ; 

 a substance which is not fluid, but organized, which possesses 

 an extremely complex structure, and is transmitted from one 

 generation to another. 



But this view did not decide the question whether the ovum 

 was not, after all, vitalized by fertilization. O. Hertwig was 

 obviously still under the influence of this idea when in 1885 he 

 maintained in the above-mentioned work, that ' the fertilizing 

 substance transmits, at one and the same time, those peculiarities, 

 which children inherit from their parents.' Such an explanation 

 is, in a certain sense, defensible, and we may speak of a ' fer- 

 tilizing substance,' in so far as the amounts of nuclear material 



