328 
0. DEBAISIEUX. 
and we find them to be invariably inherited through the 
eofg-.” 1 
oO 
It is to verify the accuracy of this last opinion tliat I have 
again taken up the expei'imeiits of hybridisation of Ecliinus 
miliaris, esculentiis and acntus. The animals which we 
used were collected at Plymouth and sent to London, where 
they always arrive perfectly fresh and in a fit state to give 
good fecundation. I used methods wliich were advised by 
Professor MacBride, and which he himself has described in 
two articles (’03, ’ll). I have only to add that the niosr. 
minute precautions were taken to avoid errors of any descrip- 
tion. Tlie animals were carefully washed in fresh water 
before being dissected ; all the instruments and utensils wei'e 
sterilised before use; sea- water was never used unless it had 
been kept for a long time in the laboratory and filtered 
through a Berkfeld filter. 
I principally concentrated my attention on three charac- 
ters which are very characteristic of the species and easy of 
observation. 
(i) The posterior epaulettes which are present in Echinus 
esculentus and acutus, absent in Echinus miliaris. 
(ii) The posterior pedicellaria which is present in Echinus 
esculentus and acutus, absent in Echiniis miliaris. 
(iii) The green pigment which is absent in Echinus 
esculentus and acutus, present in Echinus miliaris. 
It is noticeable that, starting with these three characters, it 
is impossible to distinguish the larvm of Echinus escu- 
lentus and of Echinus acutus. Besides, no differential 
character has been recorded in these larvae. The hypothesis 
that they are two varieties of the same specie becomes more 
and more probable. Besides, the results which I obtained 
were identical whether I used E. esculentus or E. acutus. 
‘ A letter from Shearer, De Morgan and Fuchs, which appeared in a 
recent number of ‘ Nature,’ June 27th, 1912, states that this year's 
experiments give results which are quite different from those of other 
years — results which ai'e doubtless in a great measure analogous to those 
which we have obtained. I shall discuss their opinion regarding this 
variation farther on. 
