«9 



The above interpretation of the phenomenon of coloration 

 in Thais lamellosa would bring the conditions observed in these 

 snails in line with the heredity of color patterns in other groups 

 of animals in which definitive breeding experiments have been 

 conducted. This interpretation would also appear to find con- 

 firmation in the discovery by Dr. H. Staiger of the genetic 

 system of ThaiSy in which a group of secondary chromosomes 

 through the translocation of their genie elements, make poss- 

 ible a wide range of variation in the phenotypes. 



THE ISOLATING SYSTEM 



I. The life history. 



In Thais lamellosa, as in other members of the subgenus 

 Nucella (Polytropa of some authors), the eggs are deposited 

 in small vase-shaped capsules attached to the rocky stratum 

 inhabited by the parent forms. The number of eggs contained 

 in an individual capsule has not been counted, but is obvious- 

 ly very great. The relatively small number of embryos that 

 complete their development within a capsule pass through the 

 veliger stage, corresponding to the free swimming larval form 

 of most gastropods, emerge as active, crawling young snails. 

 The lack of a planktonic larval form tends to greatly restrict 

 the dispersal of the snails; presumably the principal agency 

 bringing about dispersal is the action of storms, which may 

 break loose some of the egg capsules containing viable young 

 and cause them to drift to suitable locations. 



II. Shore conditions. 



The normal habitat of lamellosa is upon rocky shores that 

 provide an abundance of barnacles, which form their principal 

 food supply. Mussels are also usually present in such areas, 

 and may form an important clement in their diet. The snails 

 are also to be found in areas where masses of immobilized 

 shells are present, such as occur in many oyster beds. The 

 piles driven to support docks frequently support colonies of 

 Thais. 



