320 
PROF. E. W. MACBRIDE. 
mass of mesenchyme can be detected in tlie normal larva 
before the antero-lateral arms have developed at all, and 
in many of the hybrids the antero-lateral arms are well 
developed. The absence of the aboral spike is therefore 
not a mere consequence of stunted growth, but is due to 
paternal influence. Moreover, it is not possible to reconcile 
the facts just recorded with any theory of dominance such as 
that put forward by Loeb, Redman, King and Moore. 
If any clear meaning be attached to the word “dominance,” 
it must signify that there is <a certain factor which may be 
present or absent in a germ-cell, but which, when it is 
present, produces in tlie resulting embryo a cei-tain chamcter. 
Now if we take the question of the skeletal rods supporting 
the aboral arms, these are normally single in Echinus and 
latticed in Echinocardium. When these two species are 
crossed we do not always find either single or latticed bars, 
but we find, as a niatter of fact, every intermediate condi- 
tion of affairs. To alter the significance of the word 
“ dominance” in such away as to make it include phenomena 
like these is, in my opinion, to empty it of all its meaning. 
Zoological Laboratory, 
Imperial College of Science and Technology; 
.Tune 2.5th, 1912. 
lilST OF W^ORKS REFERRED TO IN THIS PaPEK. 
1. Boveri.^ — -“Ein gesclilechtlich erzengter Organismus ohne uiiitter- 
liche Eigenscliaften,” ‘Ber. Ges. Morph, n. Phys.,’ Munich, 1889. 
2. “Ueher die Befrnchtimgs- nnd Eutwicklungsfiihigkeit 
kernloser Seeigeleier nnd idier die Moglichkeit ihrer Bastardie- 
ruug,” ‘Arch. Ent. mech..’ vol. ii, 1895. 
3. “ Ueber den Eiufluss der Sainenzelle auf die Larvencharaktere 
der Echiniden,” ibid, vol. xvi, 190.3. 
4 Doncaster. — “ Experiments in Hybridisation, with Special Reference 
to the Effect of Conditions on Dominance,” ‘Phil. Trans. Roy. 
Soc. (Loud.),’ series B, vol. cxcvi, 1903. 
5. Driesch. — “ Ueber rein niutteidiche Chai'aktere an Bastard-larven 
von Echiniden,” * Arch. Ent. mech.,' vol. vii, 1898. 
