1877.] 197 [Garman. 



The following candidates for membership were then 

 elected : — 



Honorary Members : Prof. Thomas Henry Huxley, Dr. 

 Joseph D. Hooker, Mr. George Bentham, London ; Prof. Dr. 

 Albert von Kolliker, Wtlrzburg. 



Corresponding Members : Dr. W. K. Brooks, Baltimore ; 

 Dr. L. de Koninck, Brussels; Dr. Carl L. Zittel, Dr. W. 

 Waagen, Munich ; Prof. Albert Gaudry, Paris ; Dr. H. J. 

 Carter, London ; Prof. Oscar Fraas, Stuttgart. 



Associate Members : Mr. Edward Atkinson, Misses A. R. 

 Curtis and H. E. Freeman, Messrs. Charles A. Houghton, H. 

 D. Minot, John B. Sweet, Mr. and Mrs. Wm. H. Sawtelle. 



The following paper was read : — 



On the Pelvis and External Sexual Organs of Selach- 

 ians, WITH ESPECIAL REFERENCES TO THE NEW GENERA 



Potamotrygon and Disceus (with Descriptions). 

 By S. W. Garman. 



In an endeavor to get at the significance, extent and limits of ev- 

 olution, from physical causes or in consequence of selection, voluntary 

 or enforced, it becomes necessary to study variation in forms, the 

 structure of which renders them more susceptible to modification 

 from changes in the influences which surround them, — forms 

 which represent the more plastic stages of animals which at a later 

 date acquire greater degrees of stability. Influenced by such an 

 idea, a study of special organs in cartilaginous animals proceeds with 

 constant question as to how a bony individual under similar condi- 

 tions would be affected in its cartilaginous stages, or how the genus 

 would have stood had its development been stopped before it attained 

 the less impressible bony structure. An abstract of the facts noted 

 during a study of this character is presented below. Attention is 

 called to the comparative amount and character of variations in one 

 or more organs among the genera of a well defined class that is with- 

 out close resemblances to others which might be mistaken for genetic 

 relations. 



To prevent misapprehension, it may be well to state myself quite 

 unable to adopt either "the theory of evolution as commonly ac- 



