No.401.] DEVELOPMENT OF PENNARIA TIARELLA. 405 
determined organization of the egg as that a given part must 
necessarily determine a given organ or part. For in the half 
or fourth embryos the number of tentacles arising in the polyp 
was of the same number and arrangement as in the normal one. 
So, too, in the formation of perisarc, rate of growth, etc., 
there was nothing to indicate that the larva was other than a 
normal one in every respect, that of size alone excepted. 
It may not be without the range of these facts to refer in 
passing to similar experimental work by Driesch, Wilson, Loeb, 
and others and to refer in particular to that which is in some 
respects rather unique. Concerning the capacity of portions 
of eggs regularly to develop into perfect embryos it is unnec- 
essary to make special mention at this time. Loeb has shown 
(93) that under the unusual stress of osmosis, induced by vary- 
ing the density of the medium, double or multiple embryos of 
sea urchins might be produced almost at will. This has since 
been matter of common experiment. What seems to me of 
special note in connection with these experiments on Pennaria 
is that not only may such experimental results be obtained, but 
that similar results have been obtained in perfectly normal 
ways, that the entire phenomena of cleavage reproduce at some 
phase or other an almost identical counterpart of former experi- 
mentation along these lines. No one can follow the segmen- 
tation of the ova of Pennaria in its extremely variable and 
anomalous aspects without the conviction that there are here 
involved intrinsic forces, quite as pronounced as any which 
have been involved in the artificially operative chemical and 
physical agents to which reference has been made. That they 
may comprise much of chemistry and of physics is not ques- 
tioned. But if so, they are intrinsic and integral. 
SYRACUSE UNIVERSITY, 
March 1, 1900. 
