174 The Naturalist of Cumbrae. 



Mr. Robertson at once satisfied Professor Koelliker's 

 mind on the subject by asking him to consider what 

 proportion in the ocean itself the whole bulk of the 

 vegetation bore to the whole mass of the water. The 

 fact is that in an aquarium the microscopic algse 

 which grow without any intentional cultivation on 

 the sides of the vessel are quite sufficient vegetation 

 for all sanitary purposes in the colony. 



Some years earlier than this Robertson had been 

 corresponding with P. H. Gosse on the habits and 

 peculiarities of a sea-anemone and a hermit-crab 

 which enter into a very curious partnership. 



Gosse, in his " History of the British Sea-anemones 

 and Corals," 1860, describes the cloak anemone, 

 Adamsia palliata, as always selecting for its support 

 the inner lip of some univalve shell, the shell chosen 

 being always, he believed, tenanted by the same 

 species of hermit, Pagurus Prideauxii. The only 

 instance in which he had ever heard of the Pagurus 

 being found dissociated from its friend was one com- 

 municated to him by Mr. Robertson. 



He mentions that the Adamsia itself in early life 

 has the power of shifting its quarters, and among the 

 evidences of this he says, "While writing this article, 

 Mr. D. Robertson sends me accounts of two in his 

 possession which manifested the same propensity. 

 Between the anemone and the shell to which it is 

 affixed there is often a little horny film of membrane 

 invariably extending beyond the margin of the lip, 

 making, as it were, an adventitious continuation of the 

 shell, and following the same general spiral direction." 

 " From several specimens," Mr. Gosse continues, 



