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structures, we must turn back to the first remarks upon the order. 

 The apertures and forms of the retrogressive shells all show that 

 they were exceptional, that they had neither well-developed arms 

 for crawling nor powerful hyponomes for swimming; that, in other 

 words, they could not have carried their spires in any of the ordi- 

 nary ways. Their habits, therefore, must have been more or less 

 sedentary; and like the sedentary Gastropoda, Fissurella, Patella, 

 etc, as compared with the locomotive forms, they presented degen- 

 eration of the form and structure of their more complicated ances- 

 tors. Their habits did not require the progressive grades of struc- 

 ture, and they dispensed with or lost them ; and in many cases this 

 took place very rapidly. This retrogression was in itself unfavor- 

 able to a prolonged existence ; and the phylogerontic nature of the 

 changes tells the same story, and one can attribute their extinction 

 to the unfavorable nature of their new habitats, and also call them 

 pathologic types without fear of misrepresenting their true relations 

 to other forms. 



II. Principles of Bioplastology. 



Relying upon the results of such researches as are described 

 above and especially upon those of Cope, Ryder and Packard, I 

 have in a former publication used the name Bioplastology to desig- 

 nate that branch of research which deals especially with the char- 

 acteristics of development and decline in the life of an individual 

 and endeavored to show that correlations exist between these and 

 the life history of the group to which the individual belongs. In 

 order to classify this branch of research properly it is necessary to 

 separate it from other allied modes of studying organic phenomena.* 



AUXOLOGY OR BATHMOLOGY.f 



Mr. Buckman and Bather, both well known for their original and 

 instructive researches on Paleozoology in England, have recently, 

 in a joint paper under the title of "The Terms of Auxology,"J 

 criticised the nomenclature employed in my papers to designate the 

 stages of growth and decline in the individual. They have also 



* The author has given a synopsis of the facts that seem to characterize the different 

 branches of research and their relations to Bioplastology in a paper entitled, " Bioplas- 

 tology and the Related Branches of Biologic Research," Proc. Bos. Soc. Nat. Hist, xxvi, 

 pp. 59-125 ; and a brief preliminary abstract appeared in Zool. Anzeiger, Nos. 426, 427, 1893. 



t Cope, Proceedings Phil. Soc., Phila., Dec, 1871, and Origin of the Fittest, p. viii, etc. 



X Zool. Anz., Nos. 405, 406, 1892. 



