EXPEEIMENTAL HYBEIDISATION. 327 
111 another set of experiments on Sph^rechinus and 
Strongylocentrotns, Yernon (’00) notices considerable varia- 
tions in the hybrids which he obtained. 
At times they present characters which are almost exclu- 
sively maternal, at others almost exclusively paternal, and 
again, at times, characters more or less approaching one or 
the other. These results are confirmed by Steinbriick (’02), by 
Doncaster (’04), and by Herbst (’06 and ’07), but whilst Yernon 
attributes these variations to the influence of the seasons, the 
last authors, above quoted, are more precise, and attribute 
them to the changes in the temperature. 
Equally contradictory results were given by the crossings 
of other species. Hagedoorn (’09) studied only one cha- 
racteristic of the skeleton of the hybrids of Strongylocen- 
trotus franciscanus and Strongylocentrotus purpu- 
ratus. He discovered a purely maternal heredity; on the 
other hand,Loeb, King and Moore (’10) and Moore (’12), taking- 
up the same study notice that the different characters of the 
skeleton of the hybrids are not of maternal origin, but always 
follow the law of dominance, that is to say that the same 
character is always present or absent in the hybrid, whether 
it is F. ? X P. or P. $ x F. (^ . 
Yery similar conclusions were drawn by Tennent (’10) in 
his experiments in crossing Hipponoe and 'I’oxopneustes, but 
he remarks tlmt the characters which follow the law of 
dominance vary according to the alkalinity of the water 
which is used in the experiments. 
At last we come to the experiments of Shearer, De Morgan, 
and Fuchs (’ll). After examining the hybrids of Echinus 
miliaris, esciilentus and acutus, the authors conclude: 
A. “ There is considerable evidence for the contention put 
forward by Loeb, King and Moore (’10) that the minor 
skeletal characters are inherited independently from either 
parent. 
B. “ In the presence or absence of the posterior ciliated 
epaulettes, of the green pigment masses, and of the posterior 
pedicellaria, we claim that we have found definite characters. 
