PATERNAL CHARACTERS IN ECHINOID HYBRIDS. 339 
During 1909-1911 no exceptions were found to this rule of 
maternal inheritance, and in the present year the crosses 
E. esculentus $ x E. miliaris cj and E. acutus $ x 
E. miliaris c? have behaved as before. It is, however, in tlie 
hybrids with E. miliaris $ that we have obtained different 
results. All the cultures of E . m iliaris ? x E. acutus 
have sliown a paternal inheritance, dhius, in PI. 18, fig. 7, 
the gi'een pigment ot E. miliaris is absent, while the pos- 
terior epaulettes of E. acutus are present. Again, in the 
cross E. miliaris ? X E. esculentus (5*, with an e.xcep- 
tion, all the fertilisations gave paternal larvje (PI. 18, fig. 9). 
It seems, then, that it is the E. miliaris eggs which are this 
year in general unable to transmit the characters of the 
species to the hybrids. 
In former years cultures of E. miliaris have always shown 
a more rapid rate of growth in the laboratory than the other 
species. 'I’his, we have suggested in our preliminary paper, 
is possibly due to the fact that, E. m iliaris being a shore 
form, laboratory conditions may be more suited to it than to 
E. esculentus or E. acutus, the habitat of which is in 
deeper water. Not only did E. miliaris develop rapidly, 
but any crosses into which it entered had their rates of growth 
accelerated. 'I'his year, however, this species can only be 
obtained in a late stage with great difficulty, and its rate of 
growth is slower than that of E. esculentus, E. acutus, or 
any of the hybrids.^ With regard to the latter, when E. 
miliaris is used as the male parent, fertilisations can easily 
be made, and the inheritance is, as usual, maternal. When, 
however, E. miliaris eggs are used in the cross, only a very 
low percentage are fertilised, and the inheritance is, as stated 
above, paternal. A few exceptions only have been found to 
this. Jn one experiment only a high percentage of the E. 
‘ Since the above was written tliis matter has been brought up at 
the Dundee meeting of tlie British Association. Prof. MacBride stated 
there that lie had tliis year bred E . miliaris, obtained from Plymouth, 
at the Imperial College of Scieiu-e in London, and that the larvae could 
lie raised as easily as in former years. 
