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-epitheliomata found 

 occasionally in human sexual glands also owe their origin to the 

 beginning of a pai^henogenetic 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- 

 jmratus 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. 



