2 FRANK R. LILLIE. 



fertilisin. If there is such a connection between the capacity of 

 the eggs for agglutinating spermatozoa and for being fertilized, 

 then, in addition to other consequences which have been followed 

 out by Just (1919), Moore (1916, 1917) and the writer (1914, 

 1919), the fertilization reaction and sperm agglutination should 

 show a similar degree of specificity. This has been shown to be 

 the case in wide crosses, as between Arbacia and Nereis by the 

 writer, and between Arbacia and Echinarachnius by Just. But 

 the matter has not been tested with two species of a single genus 

 where the test might be expected to be crucial. If there were no 

 connection between agglutination of spermatozoa and fertilization 

 of the egg, the phenomena need not exhibit similar specificities; 

 but if the phenomena were found to be similarly specific we would 

 have a new and strong argument for the postulated connection. 



The problem of specificity in fertilization is at present obscure, 

 and in any case data presenting the nature and degree of spe- 

 cificity could not fail to be useful. It is rather extraordinary 

 that no attempt to secure even roughly quantitative results on this 

 problem in animals has hitherto been recorded. 



In the neighborhood of Pacific Grove, California, Strongylo- 

 centrotus purpuratus and 5\ franciscanus are found in protected 

 situations along the rocky shores. S. purpuratus occurs a short 

 distance below the high-water mark and extends to an unde- 

 termined depth, certainly several feet, below the low-water mark. 

 S. franciscanus rarely occurs above the low-water mark and cer- 

 tainly extends into deeper water than purpuratus. At low water 

 one thus finds purpuratus in isolated tide pools and sometimes 

 entirely exposed, whereas franciscanus is very rarely found in 

 such situations. The two s.pecies are commonly, though by no 

 means always, intermingled just below the low water mark. In 

 one collecting station purpuratus was so abundant in this zone 

 as to form a veritable pavement on the floor and a covering on 

 the sides of the partially open rock-pool ; S. franciscanus, very 

 conspicuous by its larger size, longer spines and different color- 

 ing, was interspersed among the individuals of the other species. 



At the time of my visit, January and February, 1920, both 

 species were ripe simultaneously at this station and elsewhere; 

 but whereas all individuals of purpuratus had practically only 



