95 
The Nucleus and Heredity. 
not then be accepted. Later, Godlewski (1906) made further 
observations on hybrid eggs of Echinoderms. He carefully sorted 
out the enucleate egg-fragments of Echinus, and found that on 
crossing them with the sperms of Antedon the larvas showed in 
their young stages purely maternal characters, whether they arose 
from such fragments or from normal eggs. The merogonous larvae 
unfortunately only lived a very short time, none of them proceeding 
beyond the gastrula stage, but the evidence certainly does show 
that, in some cases, the cytoplasm alone of the egg is able to 
impress upon the embryo, at least in its early stages, the purely 
maternal characters. 
It is important, however, not to lay too much stress on these 
experiments, significant as they are. Godlewski himself does not 
claim that they in any way cast doubt upon the importance of the 
nucleus in the hereditary processes; all they do is to supply evidence 
that the protoplasm of the egg also plays a part in these processes. 
It must also be remembered, as already mentioned, that the proto¬ 
plasm of the egg has been associated with the female nucleus during 
all the stages of maturation, so that at the time of fertilisation 
changes may have already been initiated in the egg (as the result of 
nuclear activity) which have already laid down the lines of early 
development. This would seem also to be the explanation of those 
cases in which removal of portions of egg-protoplasm cause deformity 
in the embryo resulting after fertilisation. The elegant experiments 
of Fischel (1897) may be mentioned, in which removal of different 
portions of the egg of Beroe caused different malformations in the 
embryos. There is no reason to doubt that these substances 
were produced under the influence of the female nucleus, nor is 
it surprising that in the absence of suitable materials to be activated 
certain organs should fail to develop even though the whole 
complement of hereditary properties is present in the nucleus. 
Against the experiments of Godlewski we can set those of 
Herbst and Boveri. Herbst (1906-9) has made ingenious experiments 
on echinoderm eggs which were fertilised by a foreign sperm after 
they had been caused (by an artificial increase in the osmotic power 
of the surrounding medium) to start developing parthenogenetically. 
The start in the direction of parthenogenetic development led to 
an increase of the substance of the female nucleus relatively to that 
of the male nucleus, and it was found that in such eggs the 
development was shifted in the maternal direction, i.e., the embryos 
were more like those of the female parent than they would have 
