54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, I25 



tenuicula Gould, of the west coast of America. The yellow color which appears 

 on the surface like an epidermis, and the shape, serve as a guide to this form. 



Among the Pyramidellidae it seems to be the rule, that the most variable 

 forms are the most abundant and most widely distributed. This leads one to 

 wonder if it is not the optimum condition that weakens specific bonds and tends 

 to throw an organism into the so-called "state of flux" rather than the reverse. 



It is interesting to note that these "stages of flux" are not confined to moUusks 

 but are found in many groups of plants and animals, and are put to human use 

 by breeders. 



The explanation for the phenomenon was furnished me by a colony 

 of Bahama Cerions (land shells) which I had planted on the Florida 

 Keys. Here I had placed, in 191 2, colonies of 500 of Cerion viaregis 

 Bartsch and Cerion casablancae Bartsch on alternate keys, from Miami 

 to the Tortugas, in the hope that these would tell whether the enor- 

 mous numbers of species of Cerions in the Bahamas were constant in 

 their characters or varied with varying environments. 



It was held by some of our foremost malacologists that a wet year 

 might produce giants and a dry year dwarfs. 



My planting proved first of all that Bahama Cerions required three 

 years to gain maturity. Then they showed no change of form or 

 color throughout the range of Florida Keys, But on two of the keys 

 I met with a great surprise in 1914 and 1915. A hurricane had passed 

 over the central portion of the chain of islands prior to my planting 

 and had evidently swept away the native Florida Cerion incanum 

 from the grass-covered beaches. Here I found on New Found Harbor 

 Key, on a single bush, a number of Cerions entirely unlike the C. 

 viaregis that I had planted there. Also I found among this colony 

 quite a number of C. incanum that had evidently been buried under 

 sand by the storm when I did my planting and thus escaped my notice. 

 Next year I found many more hybrids in this colony. 



In 191 5 I found a similar condition in the adjacent colony on 

 Boca Grande of the much larger white Cerion casablancae Bartsch. 

 These hybrids also showed, upon dissection, that the anatomy of the 

 soft parts presented by different individuals was as varied as the 

 characters presented by the shell. One dissection showed even a 

 duplication of the sexual organs. 



Later plantings of individual pairs of the Florida and Bahama 

 species, in cages and water-bound plots, confirmed the hybrid theory. 

 This work was carried on under the joint auspices of the Smithsonian 

 Institution and the Marine Biological Laboratory of the Carnegie 

 Institution at the Tortugas. In one of my reports to those institutions 

 I suggesed "Hybridisation, Mutation, Isolation, Fixation, Speciation" 

 as a method of producing new species. 



