8 JOURNAL OP MARINE ZOOLOGY AND MICROSCOPY. 



was adding to its shell. Ere long two things were apparent. First, 

 the new shell was paler in colour than the old, and second, that the 

 recently added portion was at a different angle to the original, so as 

 to cover a larger surface, thus _^-/\ — . 



As the animal moved about, the shell was slightly raised from 

 the surface, and owing to the double curve of the glass, it was 

 evident it had to be raised more than was convenient or desirable. 

 When the shell was widened it did not need to be raised so much. 



This limpet lived a considerable time in this small vessel, and 

 having now gained a little experience I ventured upon a further 

 experiment. I procured a large propagating glass, had a stand made 

 to fit the curved and knobbed end, and then had an Aquarium of 

 considerable dimensions, holding several gallons of water. The glass 

 formed only a single curve, the vessel being circular in shape, but 

 the sides being straight. As soon as the sides had a coating of green 

 I transferred the limpet to it. Here it lived for several months, 

 during which time it again added considerably to its shell, and again 

 the addition was at a different angle. /\__ 



Not so obtuse as the previous enlargement, nor yet so acute as 

 the original shell. The change of angle was very distinct in each 

 instance. 



This I considered to be further evidence in support of the 

 previous suggestion, that the shell was made wider so that the 

 organs should not be unduly strained to raise it from the convex 

 surface. The present glass, though not by any means so level as the 

 rock on which it resided in a state of nature, had yet a curve of much 

 greater radius than that of the former vessel, and the new curve was 

 single, not double as before. Thus the changed angle enabled it to 

 assume the required position with less inconvenience. 



Was this the result of some volition on the part of the animal, 

 or was it caused by the shell-secreting organs being forced from their 

 normal position ? In any case the change of angle appeared to be 

 to the advantage of the animal, and I have no doubt were limpets 

 reared from the commencement of their lives on curved surfaces like 

 those of either of my vessels, the angle would be much greater, so as 

 to produce a flatter shell than when they live on a level or nearly 

 level rock. 



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