STUDIES OF FERTILIZATION 449 
substances, ete., but we know that constructive metabolism is 
also impossible in the absence of a nucleus, and we may conclude 
from many facts, as Conklin (12) expresses it, that ‘‘rapid and 
intimate interchange between the chromatin and the protoplasm 
is the condition of rapid metabolism and ex hypothese of rejuven- 
escence; slow interchange is the condition of slow metabolism, and 
of senescence.” It is on account of the slowness of such inter- 
change between nucleus and cytoplasm, as I believe, that the 
unfertilized egg is inhibited from development. The internal 
function of the spermatozoén in development is to restore the 
condition of active and intimate interchange between nucleus 
and cytoplasm. Aster formation and karyokinesis are evidences 
of such restoration. The sperm nucleus and egg cytoplasm are 
immediately capable on union of such interchange, and as the 
fertilization process proceeds the egg nucleus is drawn in. 
We are led, then, to the following point of view with reference 
to the internal phenomena of fertilization, viz.: in both the sperm 
and the egg cell as the result of maturation the capacity for the 
nucleo-plasmic interaction necessary for construction metabolism 
has been lost. But such interaction takes place between the 
sperm nucleus and egg cytoplasm, and this initiates the internal 
phenomena of fertilization. The egg nucleus also is drawn into 
the karyokinetic phenomena in one of two ways, either that the 
sperm nucleus has so altered the egg-cytoplasm that karyokinetic 
reaction between the egg-nucleus and its own cytoplasm can now 
follow, or that copulation of the germ nuclei results in a change in 
the egg nucleus that restores its capacity for the necessary nucleo- 
plasmic reaction. 
In his experiments on constricting fertilized eggs of the sea- 
urchin between the germ nuclei, so that the copulation of the 
latter was prevented, Ziegler (98) has shown that the egg nucleus 
becomes surrounded by cytoplasmic radiations which rhyth- 
mically appear and disappear synchronously with disappearance 
and. reappearance of the nuclear membrane. These observations 
indicate a change produced by the sperm nucleus throughout the 
egg cytoplasm, inducing partially but not completely the rhyth- 
mical series of successive karyokinetie divisions. Other obser- 
