856 MR. E. S. EUSSELL — ENVIKONMEXTAL [NoV. 26, 



3. Environmental Studies on the Limpet. 

 By E. S. Russell, M.A.* 



[Received May 30, 1907.] 

 (Text-figures 217-228.) 



Introduction. 



The ol)ject of this paper is to correlate certaiii modifications of 

 the shell of Patella vulgata with definite environmental conditions. 

 Patella is stationary ; hence if one takes a number of shells from 

 one locality and contrasts them with a number from another 

 locality, which differs from the first in certain definite respects, 

 any difierences between the two sets may be safely put down to 

 the influence of the environmental factors in which the localities 

 differ. That is true if there has been no selective process at 

 work, and since the diflferences found were slight and apparently 

 of no selective value I have assumed the absence of selection. 

 Measurements were made of several hundred shells from 

 definite localities and the ratios of the dimensions calculated. 

 Since the ratios of length to breadth (g), length to height (g), and 

 distance from apex to posterior edge to distance from apex to 

 anterior edge \^) change very rapidly with the growth of the 

 shell, it has been necessary to arrange the ratios in groups accor-d- 

 ing to the size of shell, and to calculate the mean values for each 

 group separately. 



The shells measured were collected in 1903 and 1904 at 

 W. Bennan, Arran.- A few shells of P. athletica were included. 



I desire to express my indebtedness to Dr. J. F. Gemmill, 

 rTlasgow University, whose interesting papers on sex in the 

 Limpet are well known, for much helpful criticism. 



I hope to work out from my data on a future occasion some 

 results concerning variation, laws of growth, and correlation in the 

 shell of Patella. 



I. The Homing Hahit of the Limpet. 



It has long been matter of common knowledge that a limpet, 

 when once it has taken up a fixed position on a rock, only leaves 

 that position to make short excursions for food, and returns always 

 to it. This fact may be taken as well established. 



Most of the published observations, however, concerning this 

 habit of the limpet record merely isolated cases, and many gaps 

 remain in our knowledge of it. 



There is no agreement among authors as to the time at which 

 the limpet leaves its " home " to seek for food. Lukis (10), 

 Jeflfreys (9), Peach (quoted by Jeffreys), and Robertson (14) state 

 that the limpet wanders when covered by the tide. Davis (3) 

 and H. Fischer (6) state that it Avanders while uncovered, and 



* Communicated by the Secketakt. 



