INTRODUCTION 11 



begin to develop, but then disintegrate unless the harmful 

 secondary effects of membrane formation are counteracted 

 by some further manipulation. Hence some of the sea-urchin 

 eggs treated with starfish sperm behave as though membrane 

 formation had only been caused by virtue of some haemolytic 

 substance carried by the sperm. But if these eggs are first 

 treated with starfish sperm and then, after membrane forma- 

 tion, exposed for a short while to hypertonic sea-water, they 

 can develop into larvae. The other sea-urchin eggs, however, 

 that formed membranes with starfish sperm developed into 

 larvae without the necessity for any further exposure to hyper- 

 tonic sea-water or to lack of oxygen. 



These facts are intelligible on the following assumption. 

 The spermatozoon causes membrane formation by a substance 

 which is comparatively soluble in the egg; in addition to this 

 membrane-forming substance the spermatozoon carries a 

 second substance into the egg which prevents the disintegration 

 which follows after mere membrane formation. Those eggs 

 of the sea-urchin which upon contact with the sperm of the 

 starfish formed membranes but then began to disintegrate 

 absorbed only this membrane-forming substance; while into 

 those eggs which formed a membrane and developed into larvae 

 the whole spermatozoon had entered. 



These observations upon the effect of starfish sperm on the 

 sea-urchin egg lead to the interesting problem of why the treat- 

 ment of sea-urchin eggs with their own sperm never causes 

 membrane formation alone (without complete development 

 following). For when sea-urchin eggs are fertilized with sea- 

 urchin sperm, all the eggs that form membranes invariably 

 develop, and it never happens that some begin to develop and 

 afterward decompose. The answer is that the "lysins" of for- 

 eign sperm can penetrate into the egg in two ways, by diffusion 

 or by being carried by a spermatozoon; the " lysins" of the 

 spermatozoa of the same species, however, never can get into 



