EXPERIMENTAL HYBRIDISATION. 
329 
I obtained the pure larvae for each type (figs. 1, 2 , 3 } and 
the four hybrids which are possible : 
M. $ X E. d* (fig. 4) ; E. ? X M. cj (fig'^'- 6) : M. $ x 
A. c? (figs. 7, 8) ; A. ? X M. c? (figs. 9, 10). 
I was able to rear all the hybrids of E. acutus through 
the metamorphosis until they reached the stage of the adult 
echinus. The hybrids of E. esculentus did not go beyond 
the metamorphosis. 
The heredity of the three characters which I studied was 
as follows : 
(1) The posterior epaulettes were present in all 
the larvae of the four kinds of hybrids. 
This character, therefore, was transmitted to the bastard 
larvae in each case, in some through the father, in others 
through the mother. This character, however, is not wdiolly 
transmitted to hybrids. In the larvae of pure E. acutus or 
esculentus the epaulettes are formed at the expense of the 
loop of the ciliated band which intervenes between the post- 
oral arm and the postero-dorsal arm, and then the epaulettes 
entirely separate themselves from it. Now in hybrids we have 
observed that the posterior epaulettes remain attached to this 
commissure, and do not separate themselves from it. Conse- 
quently the epaulettes are not so perfectly formed in hybrid 
larvae as in pure larvae. 
(2) The posterior pedicellaria is to be found in the 
following hybrids: M. $ xA.J',A.? xM.(?,E.? xM.(?, 
and probably also in M. ? x E. d' • Ewt the posterior 
pedicellaria is sometimes absent in certain individual larvae. 
One must notice that in the pure larvae of E. miliaris, one 
does not find a pedicellaria at the posterior pole, but a cellular 
proliferation in which a calcareous plate is formed which 
often bears a spine. Now in hybrids one sometimes finds one 
spine, sometimes two, and sometimes two spines and a 
pedicellaria. 
(3) The green pigm ent is never trail smitted to the 
larvm in any of the four kind s of hybrids. This green 
pigment is present in the larvm of Echinus miliaris in four 
