148 PATELLA THEIR HABITS. 



tained by marking one individual, to avoid mistake, and 

 then observing its cautious roaming, and regular return to 

 its favourite place of rest, where the shell will be found 

 exactly to correspond with the surface of the rock to which 

 it is attached. Here it will rest, or sleep, and only relax 

 its strong adhesion to the rock when the muscular fibre be- 

 comes exhausted by long contraction, in which state a sud- 

 den blow horizontally given will easily displace it. A fact 

 known to the fishermen and poor, who use them for food, 

 is, that they are more easily collected in the night-time than 

 in the day. May not this be the period of roaming for food, 

 as well as when covered by the tide ? 



"The march of the limpet is slow and formal; and, 

 whenever the cupping process is renewed, the posterior end 

 of the shell is brought in contact with the rock, which, if 

 of a soft nature, will receive the impressions of its denti- 

 culations." The track of an individual, placed under sur- 

 veillance, was thus made visible over a space of several yards, 

 possessing the same regularity and disposition, and was fur- 

 ther remarkable for the constant revolution on its left. 



" The tracks of the limpet on granite and other hard 

 rocks present at first sight the same appearances ; but on 

 a closer examination they are found to differ." When first 

 observed, in 1829, a large portion of a fine-grained sienitic 

 rock was traced over by these shells ; the remainder was 

 plain, and appeared varnished with a thin coating of some 

 kind of fucus, without any markings upon its surface. 

 " As no Patellae were at first discovered, and the isolated 

 situation of the rock prevented any from reaching it, I 

 was at a loss to explain these appearances ; but after some 

 search, a fissure was found at the north end, where five 

 or six limpets had fixed themselves, each having a direct 

 road leading to their pasturage -ground. By the help of a 

 glass, the markings visible on the rock were discovered to 

 be the remains of the above fucus, which had been eaten 

 through or trodden down by these animals in their excur- 

 sions, and which retained the indentures of their shells. 

 The edge of the vegetable surface was then examined, and 

 found to be nibbled in a circular manner, resembling the 

 anterior margin of the shells." * 



* Mag. Nat. Hist. iv. 347. 



