Mr. C. Spence Bate on the Development of the Cirripedia. 329 



greatest care and watchfulness, to preserve the young creature 

 alive, so as to have the successive forms through which it passes, 

 between the figure given as the earlier form with this paper, and 

 that by Mr. J. V. Thomson in his ' Zoological Researches ' upon 

 Cirripedes ; consequently there is a blank existing which imagi- 

 nation will scarcely venture to supply ; so very unlike each other 

 is the form in the earlier stage, to that which the larva or rather 

 pupa assumes immediately prior to its adopting the character of 

 a fixed animal. 



I am aware that almost as great a difference exists between 

 the very young larva of the decapod marine Crustacea and the 

 one into which it is transformed, and that many moultings of the 

 tunic must take place before the larva has arrived to the size to 

 which it must, ere it can put on its more permanent form ; so 

 likewise it may be with the Cirripedia, that the larva shall so in- 

 crease without change of form or undergoing a fresh metamor- 

 phosis prior to the one figured by Mr. Thomson and my own 

 observation. That these animals sensibly increase in size during 

 fifteen days (which is the longest period that I have been enabled 

 to keep them alive) seems to lend assistance to this supposition ; 

 yet, notwithstanding, I can scarcely suppress the notion that 

 some unrecognized form, possessing somewhat of the characters 

 of each, will be found to be an intermediate stage of the creature's 

 existence. 



It was at the latter period of its existence as a free animal 

 that it was observed by Mr. Thomson, from whose figure the 

 one given with this paper in some slight detail differs, which 

 probably has arisen from the greater or less transparency of the 

 shells belonging to the respective specimens examined. 



At this period the animal approximates much more nearly to 

 its permanent character than it had done previously, as the nata- 

 tory legs, which have increased to six pairs, together with the 

 caudal appendage, form, with the soft parts of the animal, as seen 

 through the transparent shell, a near resemblance to similar 

 parts, only less developed, which belong to the adult animal : 

 one slight exception exists in the natatory legs folding in the 

 larva first anteriorly and then posteriorly, somewhat in the form 

 of a compressed letter Z, from the last joint of which a strong 

 spine projects which remains erect after the members are folded 

 and at rest. Although six is the recognized normal number of 

 pairs of legs in this stage of the young animal's existence, yet I 

 was only capable of counting five pairs in the specimen from 

 which this drawing is taken ; — a circumstance, which might lend 

 assistance to establish the truth of the intermediate stage given 

 by Burmcister, which is figured and described as having only 

 three pairs similar to that of the larva in its earliest period ; and 



