EFFECT OF SPERM EXTRACT 205 
by mere diffusion, while the lysins of the same species cannot 
get into the egg by diffusion. Only through the motive power 
of the living spermatozoon which acts as a carrier can the ferti- 
lizing lysin of the animal’s own species get into the egg. 
If the eggs were not immune against the lysins of their own 
species, it would be inevitable that their development would be 
caused by the lysins of the blood or the body liquids of the 
female. They would all be caused to begin to develop and then 
perish, and this would cause the extinction of the species; 
or if a complete development were possible, parthenogenesis 
would be the rule. This would lead to the extinction of all 
forms of animals in which the male is heterozygous for sex, 
since the offspring would all be males. 
Leo Loeb" has published observations which make it probable 
that in the ovary of higher animals a small percentage of eggs 
can begin a parthenogenetic development. He found in about 
10 per cent of the ovaries of guinea-pigs between the ages of two 
and six months ‘“‘transitory tumors” (chorion-epitheliomata) 
which cannot be interpreted in any other way than as young 
embryos, which, however, undergo an abnormal development. 
These tumors seem to originate from eggs lying in the super- 
ficial layer of the ovary. A kind of placenta is formed. It is 
possible that the embryomata and chorion-ep:theliomata found 
occasionally in human sexual glands also owe their origin to the 
beginning of a parthenogenetic development of eggs. 
4. For the sake of completeness the following facts should 
be mentioned. When we add living spermatozoa of foreign 
species, e.g., of the shark or even of starfish, to eggs of S. pur- 
puratus in normal sea-water we do not, as a rule, get a mem- 
brane formation. But when we use the extract of dead sperm 
of these species, the unfertilized eggs of purpuratus may form 
membranes in normal sea-water, especially if the eggs have 
been previously sensitized. This difference is accounted for by 
1 Leo Loeb, Zeitschr. f. Krebsforschung, XI, 259, 1912. 
