Dr. A. Krohn on the Development of the Cirripedia. 425 



corresponding valves of the shell, in the anterior portion of the 

 ^ody, which, in the Lepadidse, afterwards becomes for the most 

 J xvt developed into the peduncle. They consist of a dark mass 

 of pigment, in which several roundish crystalline bodies are 

 deeply immersed, and of an external envelope, which covers the 

 crystalline bodies in the form of a cornea; they therefore agree 

 in structure with the eye of the Daphniadse. 



The simple eye is situated in the median line, higher up to- 

 wards the back than the compound eyes, and a little behind 

 them. It is, as will hereafter appear, the ocellus of the previous 

 period. It consists of a firm capsule filled with a mass of blackish- 

 brown pigment, but apparently no longer contains a lens, and 

 is thus reduced to a mere organ for distinguishing light and 

 darkness. In the last metamorphosis it passes into the young 

 Cirripede, and is always, as is well known, readily to be detected 

 even in fully developed Cirripedes, especially the Lepadidae. 



The six pairs of swimming feet, which are subsequently con- 

 verted into the cirri, consist of a peduncle, from which the two 

 branches already mentioned are given off; the terminal joint 

 of the latter bears several very long biplumose bristles. The two 

 appendages of the caudal process or abdomen are beset at the 

 extremity with exactly similar bristles. 



The two walking or adhering feet consist of four joints, of 

 which the third is dilated into a disk ; the very short terminal 

 joint is attached to the upper surface of the disciform joint, and 

 indeed quite to one side and at a right angle (see Darwin, pi. 30. 

 fig. 8). In walking, during which the legs are alternately ex- 

 tended and retracted, the disciform joint presses, like a sucker, 

 so firmly to the object as to enable the animal even to creep 

 up polished surfaces, such as the wall of a glass. By means 

 of the same disciform joints the young animal attaches itself to 

 foreign bodies when it is about to undergo its final meta- 

 morphosis *. 



After these explanations, I may pass to my own observations. 



I have observed the transition to the Cypris-form in two spe- 

 cies of larvse, one of which I met with in various stages of deve- 



* As Darwin has already proved, a regular cementation, by means of a 

 tenacious gluey substance issuing from the adhesive disks, takes place 

 during this adhesion. This cement is conveyed to the adhesive disks by 

 two canals (the cement-ducts), which may be traced through the axis of 

 the ambulatory feet as far as two sausage-shaped masses situated in the 

 body, which Darwin regards as the glands preparing the cement (see Dar- 

 win, pp. 116 & 122). Darwin's investigations show further that the ce- 

 mentation goes on uninterruptedly during the growth of the Cirripedia, 

 and that in proportion as the surface of adhesion (the lower extremity of 

 the peduncle in the Lepadidae, or the base of the shell in the Balanidse) 

 increases in size, the cement-apparatus also becomes further developed. 



Arm. $ Mag. N. Hist. Ser. 3. Vol vi. 28 



