METAMORPHOSES. 15 



The form of the Carapace has been sufficiently de- 

 scribed ; it consists of thick chitine membrane, marked with 

 lines, and sometimes with stars and other patterns ; it is 

 obscurely divided into two halves by a line or suture along 

 part of the dorsal margin ; these halves or two valves are 

 drawn together by an adductor muscle, in the same rela- 

 tive position as in the mature Cirripede. The part over- 

 hanging and enclosing the thorax is lined by an excessively 

 delicate membrane, obviously homologous with the lining 

 of the sack in the mature animal, and is nothing but a 

 duplicature of the carapace, rendered very thin from being 

 on the under or protected side : a layer of true skin or 

 coriuin, probably double, separates these two folds. 



Acoustic Organs. — On the borders of the carapace, at 

 the anterior end, on the sternal surface, there are two 

 minute orifices, in Z. australis *002 in diameter, some- 

 times having a distinct border round them ; the mem- 

 brane of the carapace on the inside is prolonged upwards 

 and inwards in two short funnel-shaped tubes, lodged 

 in closed sacks of the corium : within these sacks on each 

 side a delicate bag is suspended, and hangs in the mouth 

 of the above funnel ; at the upper end a large nerve could 

 be distinctly seen to enter the bag : I cannot doubt that 

 this is a sense-organ; from its position and from the animal 

 not feeding (as we shall presently see), I conclude that 

 it is an acoustic organ. 



Antennce. — These are large and conspicuous ; they are 

 attached very obliquely on the sternal surface, a little way 

 from the anterior end of the carapace, beyond which, 

 when exserted, they extend ;* they can (at least in Ibla) 



* Mr. J. D. Dana, who has examined these organs in the larvae of Lepas, 

 informs me in a letter, that in his opinion they " correspond with the inferior 

 antennae, the superior being wanting, as in most Daphnidee." He continues 

 — " I know of no case in which the inferior are obsolete when the superior 

 are developed ; but the reverse is often true." In position these antennae 

 certainly correspond to the inferior and central pair of the larva in the first 

 stage, which belong, as it would appear, to the first segment of the body ; but 

 judging from the drawing by Burmeister of the larva in the second stage, 

 I am, in some respects, more inclined to consider that they correspond to the 

 larger pair seen within the lateral horns of the carapace in the first stage. 



