METAMORPHOSES OF CIRRIPEDES. 113 



the colour of this species when alive was blue :* in L.fasci- 

 cularis the surface is punctured : in L. jpectinata it is 

 marked with curious points of various shapes, often star- 

 shaped, in parts reticulated, and confluent along the dorsal 

 margin, and in parts lined : in B. balanoides it is very 

 obscurely punctured, and in B. Hameri the punctures pass 

 into lines. The whole of what is externally visible consists 

 of the carapace, for this is produced not only backwards, so 

 as to enclose the thorax and abdomen with their appendages, 

 but also forwards, so as to overhang the whole front of the 

 animal ; and the prehensile antennae, in Lepas, Ibla, Bala- 

 nus, and probably in all the genera, can be retracted within 

 its lower edge. The protection afforded by the carapace to 

 the antennae is aided by two crests (PL 30, fig. 7, c) parallel 

 to this lower edge. The whole sternal surface is very narrow 

 (fig. 4), and is likewise protected by the carapace ; that is, 

 when the two sides are drawn together by the adductor 

 muscle. The shell, however, when thus drawn together, 

 gapes a little at the two ends, at least in the case of Lepas 

 australis. The adductor muscle, if introduced in fig. 4, 

 would have crossed close anteriorly to the basal margin of 

 the mouth ; and in fig. 2, its end on the near side would 

 have been attached under the dark caeca, which enter the 

 upper end of the stomach. The adductor is shaped almost 

 like an hour-glass, and so differs from this muscle in the 

 mature Lepas, in which it is of the same thickness through- 

 out. I may here acid that the pupa of Lepas australis could 

 swim very rapidly, and often on one side in a circle ; it could 

 walk by the aid of its antennae, but often fell over ; being 

 thus locomotive, and, as we shall immediately see, well pro- 

 vided with senses, it cannot be considered as very lowly 

 organised. 



Acoustic Organs. — Commencing at the anterior end, two 

 small elongated orifices, Atli of an inch in diameter, 

 (e 9 fig. 4, PI. 30), may be seen ; these lead, as described in 

 my former volume, into a sack, with a bag suspended in it, 

 which is provided with a large nerve, and which I believe 



* I took this species alive in the Southern Atlantic Ocean ; and, mistaking it 

 for an independent Crustacean, was much perplexed where to class it. I had 

 overlooked these specimens when publishing my former volume. 



8 



