re of a cytolysis of the cortical layer. Anything that causes this
alteration without endangering the rest of the egg may induce its
development." When the spermatozoon enters the ovum it causes some
alteration in the surface membrane of the latter which, amongst other
things, prevents the entrance of further spermatozoa. Loeb thinks that
in causing this alteration it sets up the segmentation of the ovum. That
there is a close connection between the two events seems undoubted; that
they are in relation of cause and effect seems likely. It is quite
evident that an artificial stimulus can in certain cases set up
segmentation, but never can it cause the fertilisation of the ovum. It
may very likely produce the same change in the membrane that is caused
by the entrance of the spermatozoon under normal circumstances--membrane
formation may be necessarily coincident with the liberation in the egg
of some zymose which arises from a pre-existent zymogen. But we are
still some way off any assurance that the _main_ object of the
spermatozoon in inducing the development of the egg is this surface
alteration. It may be the initial effect; very probably it is; but since
the main function of the spermatozoon must be the introduction of
germplasm from the male parent, it is too much for anyone to ask us to
believe that its _main_ function is concerned with surface alteration.

Loeb argues that the change in the surface membrane is of a chemical
character, and that no doubt may be correct; but even if we allow him
every scientific fact, or surmise, he is still, as in the other cases
with which we have dealt, miles away from any real explanation. He is
still inside his chemico-physical explanation to begin with; and, even
within that, he still leaves us anxious for the explanation of a number
of points--for example, as to the nature of the chemical process which
accompanies, or is the cause of, segmentation. We in no way press these
questions; for similar demands could be made in so many cases; we only
indicate that they are there. What we do press is this--that when an
authority comes forward to assure us that all the processes of life,
including man's highest as well as his lowest attributes, can be
explained on chemico-physical lines, we are entitled to ask for a more
cogent proof of it than the demonstration, however complete, of the
germination of an egg, caused by artificial stimulus and not by the
ordinary method of syngamy, even