Action of blood on eggs 253 
lipoids, in the cell. If this view is correct, it would be necessary to 
ascribe the fertilisation of the egg to the same process. 
The analogy between haemolysis and fertilisation throws, 
possibly, 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, eg. 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 essen- 
tially 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 (pre- 
sumably 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 meta- 
morphosis into the adult stage and since in all the experiments made 
by the writer the parthenogenetic plutei lived as long as the plutei 
produced from fertilised eggs. 
