308 
PROF. E. W. MACBRIDE. 
obvious that the supposed liybrids were really normally 
fertilised eggs whose fertilisation had been brought about 
by the accidental and unsuspected presence of spermatozoa 
of Echinus in the water employed. One cannot help Avondei-- 
ing whether some of the results recorded in the literature, cf. 
that of Driesch that 1 per cent, of Strongylocentrotus eggs 
develop when fertilised with the sperm of Spligerechinus, may 
not be due to a similar source of error. 
Once this source of error had been detected all furtliei- 
experiments in cross-fertilisation were made in sterilised sea- 
water, and every adult urchin before being opened was 
carefully washed in fresh water in order to destroy any 
spermatozoa which might be adherent to the outside of the 
test. The instruments employed were also carefully steri- 
lised after each urchin had been opened before another was 
taken in hand. New experiments under these conditions 
gave exactly the same results when Echinocardium eggs 
were fertilised with the sperm of Echinus, and I conse- 
quently feel complete confidence in the accuracy of the 
results so obtained, but when the eggs of Echinus were 
fertilised with the sperm of Echinocardium no single egg 
developed. 
Several authors, notably Loeb ( 12 ) and Godlewski ( 8 ), 
have succeeded in fertilising the eggs of sea urchins with 
the sperm of animals belonging to distinct classes, even to 
distinct phyla of the animal kingdom of Crinoidea, Mollusca, 
etc. In the case of Mollusca it has been proved that the 
sperm nucleus does not unite with the egg nucleus, i.e. the 
chromatin which the former brings into the egg is not 
included in the first karyokinetic spindle. In the case of 
Crinoids, however, Godlewski asserts that sperm and egg 
nucleus do unite, and that the chromatin of both is included 
in the formation of the first spindle. In all such cases of 
heterogeneous fertilisation the larvte are of a purely maternal 
type and show no trace whatever of the paternal influence, 
and therefore this kind of development is termed “ Entwick- 
lungs-erregung,” on the supposition that it is due to a 
