AND OF LIGHT. 231 



to the same high temperature, developed more slowly 

 the larval period taking 142 to 163 days, and the pupal 

 25 to 31 days yielded specimens having a wing meas- 

 urement of 55 to 57 mm. It would seem, therefore, 

 that high temperature may so hurry forward the time 

 of onset of the metamorphosis from larva to pupa, that 

 there is insufficient opportunity for adequate larval 

 feeding and growth, and a consequent dwarfing of the 

 adult imago. If, however, there be no curtailment of 

 the normal period of feeding, the high temperature 

 may produce a considerable increase in the size of the 

 individuals. These conclusions are supported by sev- 

 eral other observations. 



The permanent effects of temperature on size are 

 probably very considerable among many of the Mol- 

 lusca. Thus it has often been noticed that snails living 

 in cold and exposed positions are considerably dwarfed 

 in comparison with those living in warmer regions, but, 

 as far as I am aware, no exact comparisons have been 

 made. Even if this had been the case, it would not be 

 permissible to ascribe the differences to the direct result 

 of temperature, as this might have acted indirectly, 

 through the vegetation. Certain observations of Mo- 

 bius * on marine Mollusca seem, however, to demon- 

 strate the direct effects of temperature changes. Thus 

 it was noticed that the Molluscs in the Eastern basin of 

 the Baltic are much more stunted than those in the 

 Western. For instance, Mytilus edulis is only 3 to 4 

 cm. long near Gothland, whereas at Kiel it attains a 

 length of 8 to 9 cm. Also in the Eastern basin the cal- 

 careous layers of certain shells such as M ya arenaria 

 * Report on " Pomerania " Expedition, p. 138. 



