59 
greatest expectations we may then look forwards to the future 
study of artificial hybrids of Echinoderms, now that a coraparatively 
easy method of rearing such hybrids to past metamorphosis has 
been worked out. — To rear them alone to metamorphosis will, 
however, not be enough. The specific characters are not devel- 
oped as yet in the just metamorphosed Echinoderms, only in the 
grown specimens are the characters fully developed. The end, 
therefore, is not gained before the hybrids are reared to 
maturity. 
While the artificial hybrids, the larvæ, have been the object 
of very extensive and most important research, the question, whether 
there may possibly be found natural hybrids of Echinoderms has 
received very little attention as yet. How little was known here- 
of, appears from the faet that Doncaster (Op. cit. p. 49) writes, 
after having mentioned that it is possible in certain cases to rear 
hybrid larvæ beyond metamorphosis and so to obtain hybrid urchins: 
„this raises the further question of why such hybrids do not occur 
in nature“. In faet, not a single case of natural hybrids of 
Echinoderms was known at that time, though a few suggestions 
as to their existence had been set forth (Agas s iz, Bell.). This, 
however, cannot be wondered at. The necessary condition for 
recognizing specimens as being hybrids must be both a thorough 
knowledge of the specific characters of the different species and of 
the fauna of the locality from where the specimens in question 
have come. So long as we do not know the fauna of such locality 
so exaetly that we can say with certainty that a specimen with a 
hitherto unknown combination of characters cannot possibly repre¬ 
sent a new species, we cannot have full certainty for its being a 
hybrid. Especially the latter condition has still been fulfilled for 
few cases only; but also the more thorough knowledge of the 
specific characters of the different species is of comparatively recent 
date, in any case as regards the Echinoids, which especially con- 
cern us here. It is then only what might be expected that the 
