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THE AMERICAN NATURALIST [Vol. XLI 



Many other characters of the shell, such as the oiithne of the 

 spindle, and the formation of anterior and posterior canals, and 

 the development of the color pattern, have not been touched upon, 

 but they all proceed according to a uniform law of change. The 

 Countess von Linden has endeavored to show that the transfor- 

 mation of the color pattern in marine gastropods follows Elmer's 

 law, viz: longitudinal striping, spots, cross-stripings and uniform 



Orthogenesis ix Piiylp:tic Develop.ment of GASTRoroDA. 



The protoconch, the last of the embryonic stages, is far less 

 satisfactory for purposes of tracing phyletic relationship, than is the 

 conch. Nevertheless, up to a certain point, it may, I believe, be 

 confidently relied upon. That an early stage of the protoconch 

 in the majority of gastropods is of the form of a simple naticoid coil 

 with a well-marked umbilicus, has already been noted (Studies I). 

 As stated in the first of these studies this form of the protoconch 

 recalls the character of the earliest known coiled gastropod, i. e., 

 Stroparollina rcmota of the lower Cambric of the Atlantic coast 

 province. Still earlier stages in the development of the protoconch 

 show a capuloid form, which recalls the adult character of many 

 of the early Cambric shells described under various names. That 

 all of these are not primitive but that some are phylogerontic, is 

 shown by the fact that the earliest stages are enrolled while the 

 later stages are non-coiling. Sardeson^ has indeed insisted that 

 my interpretation of such forms as Platyccras primaevum etc. 

 as phylogerontic is erroneous, and he has attempted to show that 

 the forms with slightly coiled apex are more advanced than those 

 in which the apex is not coiled at all, and that the progress of 

 development is from forms without any coiling through those with 

 enrolled apex, to the close coiled types. That this is a complete 

 inversion of the mode of coiling, must be apparent when we con- 

 sider that the animal has no more power to enroll its apex, than it 

 has to unroll it. and that, .-ince the apical part is the first-built 



^The Phylosi'iiii Staiic ut the C aiubnan Gastropoda. Journal of Geology, 

 Vol. XI, p. 470-4S2. 



