DEYELOPMENT OF THE CIRRIPEDIA. 259 



pace ; for the thorax and limbs are hidden and inclosed by its 

 backward prolongation ; and, even at the anterior end of the 

 animal, the narrow sternal surface can be drawn up, so as to 

 be likewise inclosed." The larva, in this stage, is provided 

 with two large compound lateral eyes, while the median eye 

 is arrested in its development. The oral tubercle exhibits all 

 the gnathites of a Cirripede, but they are covered by an imper- 

 forate integument, so that this " locomotive pupa," as Mr. 

 Darwin terms it, is unable to feed. There are six pairs of 

 legs, and the thorax ends in an abdomen, consisting of three 

 somites terminated by two caudal appendages. There is no 

 penis. The most remarkable structures in the pupa, however, 

 are the "gut-formed glands," which are already well devel- 

 oped, and from which the cement ducts can be traced to the 

 disks of the antenniform organs, on the faces of which they 

 open. The pupa, after swimming about for a while, at length 

 selects its permanent resting-place, to which it adheres, at 

 first, only by the action of the suctorial disks. The tempo- 

 rary attachment, however, is speedily converted into a per- 

 sistent one, the cement pouring out from its excretory aper- 

 tures on the disks, and firmly gluing them and the anterior 

 end of the body down to the surface on which they rest. 



Coincidently with these changes, several other important 

 alterations take place, during the passage of the locomotive 

 pupa into the fixed young Cirripede. The compound eyes are 

 moulted, and with them the antennary apodemes, furnished 

 by the integument of the deep fold which separates that part 

 of the body of the pupa which corresponds with the beak of a 

 Daphnia^ or of a Limnetis^ from the prosoma. The fold is 

 thus enabled to straighten itself; and, as a consequence, the 

 carapace of the Cirripede, instead of remaining more or less 

 parallel with the surface of attachment, becomes perpendicu- 

 lar to it. Again, in the pupa, the axis of the carapace and 

 that of the body are identical in direction; but, during the 

 last moult, the chamber of the carapace extends forward far 

 more on the tergal than on the sternal side, separating the 

 tergal part of the prosoma from the " beak," with which it 

 was at first continuous, and thus allowing the body of the 

 Cirripede to take its final position, which is nearly transverse 

 to the axis of the carapace. 



The terga and scuta now appear as horny thickenings, 

 and, afterward, as calcifications in the wall of the capitulum. 

 The fraena and the penis make their appearance, and the 

 genitalia become developed in the prosoma and in the pe- 



