THE NAUTILUS. 143 



ious colonies fixed forms; that is, will generation after genera- 

 tion yield the same mode in measurements, or will changes in 

 the local environment from season to season affect the develop- 

 ing organisms to such an extent as to produce an unending 

 series of slight variations ? These were the problems that called 

 for a solution. The hope of throwing some light upon these 

 questions prompted the breeding experiments which were started 

 in 1912." 



Colonies of 200 each of two species from Andros, (,'erion casa- 

 blancee and C. viaregis Bartsch were originally introduced on 

 certain of the Florida Keys. In 1915, 800 C. cmssilabris from 

 Porto Rico, and in 1916, 8,317 C. uvn from Curacao were 

 planted on Loggerhead Key. The shells were marked by filing. 

 Some of these colonies have now produced a second generation 

 of Florida-grown offspring. The present paper contains records 

 of the results. In the case of C. viaregis Dr. Bartsch finds that 

 the variations in the first and second generations are entirely 

 within the range of the species in its original locality; the 

 changed environment ''has not affected them in such a way as 

 to produce such differences as one observes between the various 

 colonies in the Bahamas." C. casablancae gives practically the 

 same result. The same holds with the first Florida generation 

 of (/'. crassilabris. 



On Newfound Harbor Khy C. viaregis has hybridized with 

 the native C. incanum. The offspring show a remarkable range 

 of variation; forms near typical C. incanum and typical viaregis, 

 all intermediates between these, but also forms closely resem- 

 bling the mottled C. martensi group of the Bahamas. A state 

 of flux has been produced by cross-breeding. The experiments 

 indicate also an unusual fertility, and the suggestion is made 

 that "crossing has an energizing effect which seems to enable 

 the new product to surpass its associated congeneric forms in 

 the production of offspring." 



Dr. Bartsch suggests that during the glacial period, when the 

 low state of water united the numerous Bahaman Keys, ex- 

 tensive crossing took place, this resulting in the efflorescence of 

 new forms which we find to-day. 



A valuable section treats of the soft anatomy, which shows 



