PATERNAL CHARACTERS IN ECHINOID HYBRIDS. 349 
Echinus found at Plymouth is relatively short so that the 
crosses can be made at one season of the year only. It appears 
to be plain, however, that the relative ripeness of the germ- 
cells used in our experiments is of no account. For, during 
the four seasons of this investigation, hybrids made at the 
commencement or end of the breeding season have not 
differed from those made at the period of maximum maturity. 
Since it was in crosses in which E. miliaris was used 
as the female parent that the inheritance was different this 
year from that in pi-evious seasons, there would appear to be 
some alteration in the eggs of this species. This is borne out, 
not only by the fact that the normally fertilised eggs of E. 
miliaris develop slowly and irregularly, but also that in the 
only hybrid cross in which the percentage of fertilisation was 
high, some of the larvm showed the usual maternal inheritance. 
Since this species has failed to develop healthily it might seem 
that tlie eggs were immature and that the breeding period 
had for some reason been postponed. But even if this were 
so, previous experience has shown us that immature eggs, 
although they may give unhealthy larvte, do not alter the 
inheritance iti hybrids. On the whole it seems most probable 
that some factor in the environment has affected the meta- 
bolism of E. miliaris in its habitat this year, so that the 
condition of the female germ-cells is changed. 
In 1906 Kupelwieser (8) fertilised Echinus eggs with 
IMytilus sperm and obtained hybrid larv® which were purely 
maternal. He found, however, that the chromatin of the 
sperm had not fused with that of the eggs, so that there had 
been no true fertilisation. In the earlier stages of our inves- 
tigation this suggested to us that the invariable maternal 
dominance which we found might be a case of virtual 
parthenogenesis similar to that of Kupelwieser. Godlewski 
(6) fertilised Echinus eggs with Antedon sperm but 
obtained a result which differed from that of Kupelwieser. 
The larvai were maternal, but he showed that there had been 
a true fusion of the nuclei, the male chromatin taking an 
active pai t in the segmentation mitoses. This result showed 
