Morse.] 



286 



[April 19, 



of Buccinum in every case were found hid away in nooks, and con- 

 cealed in the cracks and crevices marking the ledge. It was clearly 

 obvious that only the smallest males could work their way in to such 

 constricted quarters for the purpose of uniting with the females, and 

 that the smaller males had the advantage over the larger males in 

 this respect, there could be no question. The true state of the case 

 was so instantly seen, that though hundreds of specimens were col- 

 lected with the object of determining whether in any case a large 

 male occurred, not a single exception was met with in which the 

 female was not being fertilized by a diminutive male. 



Shells of Buccinum undatum, male 



Shells of Buccinum undatum, female. 



The constrained position in which these were found precluded the 

 possibility of a large male with his cumbrous shell getting close 

 enough to the female in her narrow, quarters to perform the sexual 

 act. The smaller males having this advantage, have from generation 

 to generation perpetuated their dwarfed characters. 



It would seem from these facts that natural selection has worked 

 in an unusual way in producing secondary sexual characters, rarely, 

 if ever, seen in gasteropods, 



