264 LETTERS FKOM C. DARWIN, ESQ., 



bottom of a deep hole of the diameter of a pin or straw, during 

 growth the animal would be enabled to enlarge it to any extent. 

 I confess I am quite puzzled by Clitia. It appears to me, from 

 your specimens (which I must hereafter further examine), that 

 the whole of the corrosion is effected round the margin of the 

 base; that is, that no corrosion or wear goes on except round 

 the growing basal edges. Did you come to this conclusion ? I 

 cannot doubt that the shell is so fixed that it cannot move ; cer- 

 tainly there are no sharp points on basal membrane, as I have 

 formerly examined it under high power. Does not your fact of 

 the Modiola show that the action is effected by solution, or at 

 least not mechanically. 



You ask me about Goodsir's male Balanus. It is quite a mis- 

 take. His male Balanus is a, female crustacean allied to Bopyrus, 

 and his parasite is the male of this female. 



But now comes the odd case. I have found two genera of 

 Cirripedes with males separate and parasitic on the females. In 

 these cases I am sure there can be no mistake, though I will not 

 take up your time with details. 



I have not yet ! looked at Alcippe, for ever since writing last 

 to you, my two-hour-per-day work has been occupied with a 

 tiresome set of fossils. I have the curious Alepas squalicola sent 

 me from Copenhagen, but I have not looked at it yet. 



Yours very sincerely, 



C. Daewin. 



No. 10. 



(No postal date. " 1851 " by A. H.) 



Down Farnborough, Kent, 



June 8th. 

 Dear Sir, 



I am going to beg you to endeavour to procure me a 

 very great favour from Mr. Alder, namely, the loan of the volume 

 or of the plate of Loven's Alepas squalicola, of which he most 



