Variation Induced in Brachiopods by Environmental Conditions' 



Henry M. Du Bois, 

 University of Illinois, Urbana 



In classifying fossil brachiopods the paleontologist frequently finds 

 forms that are intermediate between two allied species, and even at times 

 between closely related genera. Often transitional forms grading from the 

 parent stock to the new species are found, thus conclusively showing their 

 evolution. He is sometimes at a loss for a classification for these forms, 

 and, perhaps in some cases, several species have been made of the variations 

 of one species. 



For some time the writer has been interested in these variations and 

 has been seeking to find what causes would bring about such changes, and 

 where the division lines between species should be drawn. The fact that 

 similar variations are found, to a greater or less degree, in many different 

 species, led to speculation as to whether they were caused by similar con- 

 ditions of environment, and whether environment was the sole cause of these 

 variations, or whether there was an innate tendency in the individuals to 

 develop along certain lines. 



Several papers on variation in brachiopods have been published, varia- 

 tions have been measured and curves plotted to show the tendencies and 

 amount of the variation. In one case" variation was ascribed to innate 

 tendencies in the individual, but in the other papers''' no causes were sug- 

 gested. 



It was evident that the first step in solving the problem of the cause 

 of variation in brachiopods should be to make a study of the living forms, 

 their habits of life, and their response to the physical conditions of their 

 environment. For this purpose a trip to the San Juan region of Puget 

 Sound was made during the summer of 1915, and collections of the brachio- 



iContribution from the Puget Sound Marine Station, Vol. 1, No. 16, and 

 from the Zoological Laboratory of the Univeisity of Illinois, No. 69. 



The writer wishes to acknowledge his indebtedness to Professors V. E. 

 Shelford and T. E. Savage, of the University of Illinois, for many helpful 

 suggestions and criticisms in the preparation of this paper. Professor Shel- 

 ford also directed the work in the field and in the laboratory. 



2Wilson, Miss A. E., Museum Bulletin No. 2, Canadian Geol. Survey. 



sCumings, E. R., and A. V. Mauck, Amer. Jour, of Sci., XIV, July, 1902. 



Grabau, A. W., and Margaret Reed, 7th Intern. Zool. Cong., Proc, 1910. 



Mook, C. C, Annals of the N. Y. Acad. Sci., Vol. XXVI, 1915, 



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