Dr. A. Krohn on the Development of the Cirripedia. 425 
corresponding valves of the shell, in the anterior portion of the 
body, which, in the Lepadide, afterwards becomes for the most 
part 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 Daphniade. 
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 Lepadide. 
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, pl. 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 larv, 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 Lepadide, or the base of the shell in the Balanide) 
increases in size, the cement-apparatus also becomes further developed. 
Ann. & Mag. N. Hist. Ser. 3. Vol. vi. 28 
