1907.] 



STUDIES ON THE LIMPET. 



861 



Table IV. gives the average ratios of a like number of shells 

 collected — 200 at Station 1, 100 at Station 2 — at low water. 



Table IY. 

 Low- water Limpets. 



Li considering the difierences between the two sets of shells 

 only those between 10 mm. and 55 mm. in leng-th will be taken 

 into account, since those below 10 mm. and above 55 mm. are too 

 few to give smooth results. 



^ — This ratio is greater in low-water than in high- water shells 



for every stage except two, viz. 20-25 mm. and 30-35 mm., where 

 it is the same in both. High-water shells are therefore at almost 

 every stage a little broader than low-water shells. 



-|. — This ratio is on the whole greater in low-water shells up 



to about 40 mm., when it becomes smaller in the low-water than 

 in the high-water shells. The apex would seem therefore to be 

 further forward in low-water shells up to 40 mm. in length and 

 thereafter further back than in high-water shells. 



^. — The high-water limpets are at all stages higher spired than 

 the low- water limpets. 



?. — The high-water shells are at all stages narrower in pro- 

 portion to their height. 



As to the causes of these differences, one can say little more 

 than that they must be due to those factors in which a high-water 

 environment diflers from a low-water environment. 



58* 



