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THE AMERICAN NATURALIST [Vol. XLIX 



the same were true for the egg of Fundulus fertilization 

 could take place probably before the egg reaches the 

 bottom of the water. If by chance a teleost of a different 

 species would shed its sperm in the immediate neighbor- 

 hood and some of it could reach the egg of Fundulus 

 while it is falling the foreign sperm could probably not 

 be aroused as quickly by the egg of Fundulus as the 

 sperm of the Fundulus male and hence no hybridization 

 would occur. In fish we can see that the male and female 

 shed their sexual cells simultaneously so that they come 

 at once in contact. The writer is inclined to believe that 

 something similar occurs also in Echinoderms. He had 

 last year a chance to verify once more an observation he 

 had made for a number of years and which he had already 

 mentioned in a previous publication. 17 The sea urchins 

 at Pacific Grove are found in large numbers on rocks in 

 certain coves near the shore. Up to a certain day in 

 March every female of pur pur at us was full of eggs. On 

 the next day the surface of the sea in this region showed 

 the usual indication of the spawning of large masses of 

 animals: namely the enormous foam formation in the 

 little coves although the sea was only moderately agi- 

 tated. This foam formation is due to an increase of 

 organic substances which lower the surface tension of 

 the sea water and make the foam more durable. The 

 writer realized that this might mean the end of material 

 for some time to come and indeed not a single female of 

 purpuratus of hundreds opened on that day had eggs. 

 The condition was the same for all the sea urchins col- 

 lected for two miles along the shore. During the next 

 week immature eggs began to appear again in the sea 

 urchins and in about ton days ripe eggs were again found. 

 This indicates that in this region the males and females 

 shed their eggs and sperm simultaneously. It is not im- 

 possible that among sea urchins which are found in 

 colonies on the rocks the shedding of the sexual products 

 of one or several individuals acts as an incentive for the 

 whole colony. Since the eggs fall in this case also much 



