EXUVIATION J RATE OF GROWTH. 63 



spines on the cirri (and on the maxillae) are formed within 

 the old ones ; but as they have to be a little longer than 

 the latter, and as they cannot enter these up to their 

 very points, their basal portions are not thus included, 

 but are formed, running obliquely across the segments 

 of the cirri ; and what is curious, these same basal por- 

 tions are turned inside out, like the fingers of a glove 

 when hastily drawn off. After the exuviation of the old 

 spines, the new spines have their inverted basal portions 

 drawn out from within the segments, and turned outside 

 in, so as to assume their proper positions. 



All Cirripedia grow rapidly : the yawl of H. M. S. 

 Beagle was lowered into the water, at the Galapagos 

 Archipelago, on the 15th of September, and, after an 

 interval of exactly thirty-three days, was hauled in : I 

 found on her bottom, a specimen of Conchoderma virgata 

 with the capitulum and peduncle, each half an inch in 

 length, and the former -^-ths in width: this is half the size 

 of the largest specimen I have seen of this species : several 

 other individuals, not half the size of the above, con- 

 tained numerous ova in their lamellae, ready to burst 

 forth. Supposing the larva of the largest specimen be- 

 came attached the first day the boat was put into the water, 

 we have the metamorphosis, an increase of length from 

 about - 05, the size of the larva, to an whole inch, and the 

 laying of probably several sets of eggs, all effected in thirty- 

 three days. Prom this rapid growth, repeated exuviations 

 must be requisite. Mr. W. Thompson, of Belfast, kept 

 twenty specimens of Balanus balanoides, a form of much 

 slower growth, alive, and on the twelfth day he found 

 the twenty-first integument, showing that all had moulted 

 once, and one individual twice within this period. I 

 may here add, that the pedunculated Cirripedes never 

 attain so large a bulk as the sessile ; Zepas anatifera is 

 sometimes sixteen inches in length, but of this, the far 

 greater portion consists of the peduncle. Pollicipes 

 mitella is the most massive kind ; I have seen a specimen 

 with a capitulum 2*3 of an inch in width. 



