lo THE POPULAR SCIENCE MONTHLY 



role also in bacteriology; but it can also be caused in special cases by 

 mechanical means, such as agitation or piercing of the cortical layer. 

 It may be mentioned parenthetically that foreign blood sera have also 

 a cytolytic effect, and I succeeded in causing membrane formation and 

 in consequence the development of the sea-urchin egg by treating it 

 with the blood of various animals, e. g., of cattle, or the rabbit. 



Eecently Shearer has succeeded in Plymouth in causing a number 

 of parthenogenetic plutei produced by my method to develop beyond 

 the stage of metamorphosis, and Delage has reported that he raised 

 two larvae of the sea-urchin produced by artificial parthenogenesis to 

 the stage of sexual maturity. We may, therefore, state that the com- 

 plete imitation of the developmental effect of the spermatozoon by cer- 

 tain physico-chemical agencies has been accomplished. 



I succeeded in showing that the spermatozoon causes the develop- 

 ment of the sea-urchin egg in a way similar to that in my method of 

 artificial parthenogenesis; namely, by carrying two substances into the 

 egg, one of which acts like the butyric acid and induces the membrane 

 formation, while the other acts like the treatment with a hypertonic 

 solution and enables the full development of the larvae. In order to 

 prove this for the sea-urchin egg foreign sperm, e. g., that of the star- 

 fish, must be used. The sperm of the sea-urchin penetrates so rapidly 

 into the sea-urchin egg that almost always both substances get into the 

 egg. If, however, star-fish sperm is used for the fertilization of the 

 sea-urchin egg, in a large number of cases, membrane formation occurs 

 before the spermatozoon has found time to entirely penetrate into the 

 egg. In consequence of the membrane formation the spermatozoon is 

 thrown out. Such eggs behave as if only the membrane formation had 

 been caused by some artificial agency, e. g., butyric acid. They begin 

 to develop, but soon show signs of disintegration. If treated with a 

 hypertonic solution they develop into larvae. In touching the egg 

 contents the spermatozoon had a chance to give off a substance which 

 liquefied the cortical layer and thereby caused the membrane formation 

 by which the further entrance of the spermatozoon into the egg was 

 prevented. If, however, the starfish sperm enters completely into the 

 egg before the membrane formation begins, the spermatozoon carries 

 also the second substance into the egg, the action of which corresponds 

 to the treatment of the egg with the hypertonic solution. In this case 

 the egg can undergo complete development into a larva. 



F. Lillie has recently confirmed the same fact in the egg of a worm, 

 Nereis. He mixed the sperm and eggs of Nereis and centrifuged the 

 mass. In many cases the spermatozoa which had begun to penetrate 

 into the egg were thrown off again. The consequence was that only a 

 membrane formation resulted without the spermatozoon penetrating 



