y,
some light on a curious observation. It is well known that the blood
corpuscles, as a rule, undergo cytolysis if injected into the blood of
an animal which belongs to a different family. The writer found last
year that the blood of mammals, e.g. the rabbit, pig, and cattle, causes
the egg of Strongylocentrotus to form a typical fertilisation-membrane.
If such eggs are afterwards treated for a short period with hypertonic
sea-water they develop into normal larvae (plutei). Some substance
contained in the blood causes, presumably, a superficial cytolysis of
the egg and thus starts its development.

We can also cause the development of the sea-urchin egg without
membrane-formation. The early experiments of the writer were done in
this way and many experimenters still use such methods. It is probable
that in this case the mechanism of fertilisation is essentially the same
as in the case where the membrane-formation is brought about, with
this difference only, that the cytolytic effect is less when no
fertilisation-membrane is formed. This inference is corroborated by
observations on the fertilisation of the sea-urchin egg with ox blood.
It very frequently happens that not all of the eggs form membranes in
this process. Those eggs which form membranes begin to develop, but
perish if they are not treated with hypertonic sea-water. Some of the
other eggs, however, which do not form membranes, develop directly into
normal larvae without any treatment with hypertonic sea-water, provided
they are exposed to the blood for only a few minutes. Presumably some
blood enters the eggs and causes the cytolytic effects in a less degree
than is necessary for membrane-formation, but in a sufficient degree to
cause their development. The slightness of the cytolytic effect allows
the egg to develop without treatment with hypertonic sea-water.

Since the entrance of the spermatozoon causes that degree of cytolysis
which leads to membrane-formation, it is probable that, in addition to
the cytolytic or membrane-forming substance (presumably a higher fatty
acid), it carries another substance into the egg which counteracts the
deleterious cytolytic effects underlying membrane-formation.

The question may be raised whether the larvae produced by artificial
parthenogenesis can reach the mature stage. This question may be
answered in the affirmative, since Delage has succeeded in raising
several parthenogenetic sea-urchin larvae beyond the metam