304 
PROF, E, W, MACmUDE. 
of the post-oi'al arms. Tennent’s most remarkable conclusion 
was that the Hipponoe influence in the hybrid could be de- 
creased and the Toxopneustes’ influence correspondingly 
increased by decreasing the alkalinity of the sea-water by the 
addition of a few drops of very dilute acid. 
Hagedoorn (9) crossed two species of the same genus, viz. 
Strongy locentrotus purpuratus and Strongylocen- 
trotus f ranciscanus, and arrived at the conclusion that 
the liybrid was in every case purely maternal in its character, 
but in a paper published a little while after (12) by Loeb, 
Redman King and Moore recording the results of hybridisa- 
tion experiments between the same two species, these 
authors state that they are unable to confirm Hagedoorn’s 
results, but arrive at the curious conclusion that certain char- 
acters appear in the hybrid whichever way the cross is made — 
are, in fact, a dominant over -correlative characters; so for 
instance the clavate aboral ends of body rods are dominant 
over the pointed form, the spherical form of larva over the 
pyramidal, the presence of the recurrent rod in the skeleton 
over its absence and so on. 
The reader will gain from the preceding review an 
impression of results of a most unsatisfactory and contra- 
dictory character as the fruit of the work of all these ex- 
perimenters. Having had considerable experience in rearing 
the normal larvae of Echinoderms, it struck me that one prin- 
cipal cause of such discordant results Avas the great variability 
of the characters relied on as distinctive of the different 
species of larvae. 
I therefore looked about for “ species ” to experiment on 
whose larvffi were distinguished from one another by clear 
and unmistakaV)le characters. 'LVo possible cases presented 
themselves to mind: first the case of the species Echi n u s 
esculent us and Echinus miliaris, and second, the case of 
Echinus e s c u 1 e n t u s and E c h i n o c a r d i u m c o r d a t u m . 
With regard to the first case, it should be noted that the 
differences between the larvae of the two species do not 
become clear until the larvae are about a month old and have 
