21 



In his second paper Colton dealt with the environmental 

 relationships of Thais as regards form, size, sculpture and the 

 character of the aperture. He had available material from io6 

 localities represented by 16,000 specimens. He was inclined to 

 regard the size and shape of the shell as directly determined 

 by the environment; when exposed to heavy surf action the 

 shell becomes small and thin, while in protected areas the 

 shell was inclined to be larger and stouter. He regarded sculp- 

 ture as primarily determined by heredity, but explained the 

 imbricated forms on the theory that this condition had a se- 

 lective value, the roughened surface tending to retain debris, 

 and thus serve as a masking device. Observing discrepancies 

 in the existing distribution of imbricated forms he explained 

 these as a result of changes in sea-level during the Pleistocene. 



It was clearly indicated by Colton that he regarded his 

 conclusions, based as they were upon purely observational 

 data, as somewhat tentative, pending the evidences to be 

 supplied by physiological experimentation and genetic studies, 

 together with adequate cross-breeding to determine the facto- 

 rial structure. 



In three papers published during the years 1936-1938 Dr. 

 Hilary B. Moore presented a very thorough and detailed ac- 

 count of the forms of Thais lapillus found upon the coast of 

 Great Britain, including a summary of the previous work 

 done upon this species, an observational study of 25,000 spec- 

 imens derived from 67 localities, the breeding habits of the 

 snails, their growth, their food in the wild state and under 

 controlled conditions, and the presumed effects of chemical 

 and physical factors; altogether a most notable contribution. 



The first paper by iMoore (1936) is entitled "The Biology 

 oi Purpura lapillus. I. Shell Variation in relation to Environ- 

 ment." He assumes that all observable differences seen in the 

 local races must be due primarily to environmental influences. 

 In this point of view he is in conformity with previous authors, 

 since no allowance was made for the possible influence of 

 heredity as a factor initiating variation, with isolation leading 

 to the formation of inbred populations. 



