Morse.] 284 [April 19, 



arch would then be about nineteen miles and four-tenths. I give 

 this estimate for the purpose of showing still more conclusively that 

 there exists in our country to-day a geological power, which, were it 

 not confined by the rigidity of the rocks, would have sufficient energy 

 to form hills and mountains upon as grand a scale as those which 

 we now behold. 



April 19, 1876. 



The President, Mr. T. T. Bouve, in the chair. Forty-six 

 persons present. 



The following papers were presented : — 



On a Diminutive Form of Buccinum undatum 3 : — Case of 

 Natural Selection. By Edward S. Morse. 



The law of sexual selection as illustrated by Darwin, has explained 

 the many* varied features of secondary sexual characters, and the 

 reasons for their origin and persistence. Among these features are 

 the prehensile organs of the male, the weapons of offence and de- 

 fence, ornaments of various kinds, organs for call-notes, glands for 

 emitting odors, etc. A leading character and with few unexplained 

 exceptions, is the frequent difference in size between the^ sexes. 



In the struggles between males for possession, or in the struggles 

 which often happen between males and reluctant females, the largest 

 and more powerful males would more often win, and would more 

 frequently perpetuate their characters as secondary sexual features. 

 Darwin, in his "Descent of Man," has traced these marked differ- 

 ences in size between the sexes in crustaceans, insects, and in all 

 classes of vertebrates. 



Among certain lamellibranchiates, as Dr. Kirtland long ago ob- 

 served in the Unionidas, the difference in size and form between the 

 male and female is oftentimes well marked, so much so, indeed/as to 

 have led to their separation as distinct species in some cases ; the 

 female having the shell larger and more bulging posteriorly to accom- 

 modate the swollen gills when filled with eggs. 



Certain gasteropods are ovoviviparous, but few, if any, observa- 

 tions have been made on the relative size of the sexes. Jeffreys 

 observes that the male of Littorina liltorea has a smoother and more 



