23 
The subject of the essay furnishes a problem which must possess 
interest to every embryologist, even though he should reject the con- 
clusions to which observation and reflection have led me. 
In working out the complete paper so many novel and confirma- 
tory points have been met with, so much of importance in the writings 
of the older embryologists, more especially in the memoirs of JOHANNES 
MÜLLER on the Echinoderm larvae, has been unearthed, that an ex- 
tension of the original plan of the work has been rendered necessary. 
My conclusions, moreover, are so much in conflict with prevailing 
doctrines that any haste in producing the full argument would be 
unpardonable, although a preliminary sketch by way of clearing the 
ground may be justifiable. 
On a subsequent occasion an attempt would be made to show 
how the researches of recent years had, with a few notable exceptions 
(such as the works of R. S. BERGH, J. KENNEL and N. KLEINENBERG) 
tended away from rather than in the direction of a recognition of the 
fundamental fact of an alternation of generations as underlying Me- 
tazoan development, in that they have been concerned, for example, 
with unnecessary attempts at homologising the ‘“‘mesoderm” and its 
mode of formation throughout the animal kingdom. If the facts in 
support of my case should not be as complete as the published re- 
searches of the past thirty years on the ontogeny of very many ani- | 
mals might lead one to anticipate, the circumstance would have an 
obvious explanation. With the death of JOHANNES MULLER — a man 
whose brilliance as an embryologist was only surpassed by his great- 
ness as an anatomist — there closed one chapter, and that one of 
the finest, in the history of comparative embryology. 
What influence the publication of the “Origin of Species” 
had upon the subsequent progress of the science is too well-known 
to need further expatiation here. The pernicious search after pe- 
digrees, initiated by HAEcKEL, led to an era of activity during which 
every fact with no apparent bearings on phylogeny was ignored. As 
a consequence the work of MÜLLER on Echinoderms and the essay of 
STEENSTRUP on “Alternation of Generations” became more 
or less mere curiosities in the history of the science. With little 
exception embryological speculation of the past thirty years has been 
naught else than a pursuit of will o’ the wisps. 
It behoves us now to revert to the path along which 
JOHANNES MULLER laboured. 
My embryological conclusions, like those of contemporaries, have 
not hitherto been influenced by the embryological works of MULLER; 
