252 LETTEES EKOM C. DAEWIff, ESQ., 



I should have written about Lithotrya in former letter, but 

 I had hardly space, and I did not know whether you would like 

 to have my views on the point. I conclude that the Lithotrya 

 forms its own holes, from having seen numerous specimens, and 

 (four or five species) large and small, all exactly fitting their 

 cavities. The calcareous cup is indisputably (I speak after care- 

 ful examination, with dissolution in acids, etc., etc.) formed by 

 the Cirripede, and is common to most (I believe all) the species 

 of the genus. You are perfectly right that the calcareous cup 

 is never moved. But the Cirripede inhabits (as far as I have 

 seen) only cellular rocks, or corals, or shells (such as the Cirripede 

 Conia,* with large tubes), and the pupa crawls into some minute 

 cavity, and there fixes itself for ever, and then as it grows en- 

 larges the hole to required size ; this it effects by the edges of 

 the valves and of the minute scales on the peduncle being sharply 

 serrated ; and as of course the serrated edge would soon be 

 blunted, the calcareous scales on the peduncle are moulted with 

 the membrane on which they are fixed, and new sharp ones 

 periodically formed. This moulting of calcareous scales is a 

 unique case, and I have no doubt is in relation to their boring 

 necessities. I believe this is the way which my Asthrobalanus,f 

 which inhabits the Concholepas, also makes its cavities ; and its 

 outer tissue is studded with elegant minute trifid and quadrifid 

 points ; and the shell is apparently first perforated by other ani- 

 mals ; but I have got to go over this again with Asthrobalanus,' 

 but I have had the misfortune to lose nearly my whole stock of 

 specimens, of which I collected thousands, for fifteen years ago 

 in the Chonos Archipelago I described its peculiarities in some 

 detail. 



I venture to predict that if you take the outer tissue of Al- 

 cippe and clear the corium from it and place it under the com- 

 pound microscope, you will find the rasping minute points, and 

 I believe you state that it inhabits shells abounding with cavities 

 of Cliona, etc., etc. 



I am most particularly obliged to you for informing me of 



* = TetracHta, Schumacher. See Darwin's Monograph, Balanidse, p. 321. 

 t = Ci-yptophialus. Ibid. p. 563. 



