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found them to be diverse also in the time at which they liberate 

 free-swimming larvae. In both species a periodicity in this act is 

 manifested (under laboratory conditions) which is more marked 

 and definite in A. pellucidum than in A. constellatum. Tadpole 

 larvae in great numbers are set free by colonies of both species 

 at, or shortly after sunrise each day during the summer months, 

 but the "daylight swarm" appears definitely later by a few 

 minutes from colonies of A. pellucidum than from A. constellatum. 

 Colonies of A. pellucidum continue, during all hours of the day, 

 to set larvae free in considerable abundance, but colonies of 

 A. constellatum liberate very few after the initial swarm at daylight. 

 Differences of a structural and physiological nature, such as 

 are found not only in the larval, but also in the adult forms of 

 these two species, cannot be regarded as expressions of a dimor- 

 phism of a single species, induced by slight imaginable differences 

 in the environment. They are rather to be regarded as the expres- 

 sion of specific differences in genetic constitution. A. pellucidum 

 and A. constellatum although very nearly related, are both valid 

 species. 



