26 



THE ROYAL SOCIETY OF CANADA 



The soft parts of these same specimens were then dried at approxi- 

 mately 100°C. until there was no further loss in weight and their 

 weights determined. The ratios of the volumes to these weights 

 were as follows : 



It is clear from these results that the individuals grown in the 

 dark had a greater volume (to the amount of more than 50%) per 

 unit weight both of shell and of living matter than had those grown 

 in the light. This may be expressed in another way, namely, that 

 those exposed to the light had a greater mass of shell and living matter 

 per unit of volume that had those kept in the dark. As the actual 

 volume of the former was very much less than that of the latter, 

 it may be inferred that the increase in volume in those exposed to 

 light was retarded to a greater extent than was the increase in weight 

 as compared with those increases in specimens kept in the dark. 



We have no data as to the weight of the shell and of the living 

 matter in these specimens at the time the experiment was started, 

 but w^e do know their lengths. They had been living under con- 

 ditions somewhat intermediate between the light and dark extremes 

 of the experiment. If we consider that they were intermediate in 

 ratio of thickness to length and of dry weight of living matter to 

 volume between the individuals from the "light" box and those from 

 the "dark" box, we may calculate the ratio of the increase in mass in 

 the specimens kept in the dark to that in those exposed to light, 

 taking as a basis the increase in average length of the specimens. 



The specimens kept in the dark increased in average length from 

 7.5 mm. to 14.4 mm!, and those exposed to the light from 7.5 mm. to 

 9.5 mm. It can be shown that if the other dimensions increased 

 proportionately the former specimens increased in volume by an 



14.43-7.53 



amount 8.2 times as great as did the latter 



= 8.2^A 



t9. 53-7. 53 



By correcting for the greater thickness and the greater relative dry 

 weight of the specimens exposed to light it has been calculated that 



