T 
348 CRESSWELL SHEARER, WALTER DE MORGAN, H. M. FOCHS. 
tlieless tlie frequent inconsistencies between the conclusions 
of different experimenters may in part be of the same nature 
as our change in inheritance. In 1889 Boveri (2), working at 
Naples, found that hybrids of the cross Sphger echinus ? 
X Echinus were all intermediate in their characters. 
Seeliger ( 11 ) made the same cross at Trieste in 1894, but 
found that in every culture some of the larvae were paternal. 
Morgan ( 10 ) repeated the work at Naples in 1895 and sub- 
stantiated Seeliger’s conclusions. It is possible tliat the in- 
heritance of parental cliaracters in this cross does not remain 
the same during a series of years. Similarly the opposite 
results obtained with hybrids between Strongylocentrotus 
f ran ci scanu s a!id S . p u r pu ratus by Hagedroon (7) and 
Loeb, King and Mooi'e ( 9 ), who worked at Pacific Grove, Cal., 
in two consecutive years, may possibly both be correct. In 
any case our results serve to emphasise the fact that it is 
necessary to repeat the same experiments many times and to 
extend them over a considerable period. It’ tlie investigation 
had been made at Plymouth during this year alone, the con- 
clusion would pi'obably have been ari-ived at that the charac- 
ters of E . esc u 1 entus and E. acutns are dominant over 
tliose of E. miliaris. We know, however, that this has not 
been the case in preceding years. 
Vernon ( 14 ), working at Naples in 1900, found that the 
inheritance in hybrids between Strongylocentrotus and 
Sphae rechin ns was different according to the time of year 
at which the crosses were made. In spring the hybrid larvte 
resembled Strongylocentrotus, while in summer they 
were like Sph re r ech in u s . Strongylocentrotus was 
found to be much riper in the spring than in the summer, and 
accordingly Vernon concluded that the dominance of the one 
species over the other was controlled by the relative rijie- 
ness of the sex cells used to make the cross. Doncaster (3), 
however, found that the cause of the change in inheri- 
tance was the difference in temperature at the two seasons. 
We cannot compare our results strictly with those des- 
cribed above. The breeding period of the three species of 
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