424 Dr. A. Krohn on the Development of the Cirripedia. 
a prominent lens and enveloped in dark pigment, shines through 
from the interior of the body. This ocellus rests upon the 
middle of the anterior margin of a distinctly marked structure, 
closely applied to the ventral surface, and surrounding the ceso- 
phagus like a ring (PI. VII. fig. 3), which I can regard as nothing 
but the central mass of the nervous system or as the cesophageal 
ring. The swimming feet, of which the foremost pair are simple, 
the intermediate and hinder pairs divided into two branches, 
are abundantly beset with long bristles, part of which are simple, 
part delicately plumose (fig. 2). In the middle of the extremity 
of the proboscidiform process is the mouth, leading into a narrow 
cesophagus, which extends through the axis of the process, and 
penetrates into the body through the orifice of the cesophageal 
ring. The rest of the alimentary canal passes straight through 
the body, swells in the middle of its course into a roundish dila- 
tation, and terminates in an anus, situated dorsally at the base 
of the caudiform appendage (fig. 2) *. 
In the second period of development, the larva, as is well 
known, is enclosed in a bivalved carapace or shell, in the same 
way as the genus Cypris. It possesses two compound eyes and 
one simple one, and is furnished on the lower surface of the 
hinder part of the body, corresponding with the thorax of the 
mature animal, with six pairs of swimming feet divided into two 
branches. At the extremity of this region of the body there is 
a short tail-like process (abdomen of Darwin), which is furnished 
with two appendages resembling the branches of the swimming 
feet. -Two other strongly developed members are particularly 
worthy of notice; these spring from the fore part of the body, 
in the vicinity of the compound eyes. With their assistance 
the larva creeps about, and it is by means of them that it finally 
attaches itself to foreign bodies, when the time has arrived for 
its last metamorphosis t+. 
The two compound eyes lie quite laterally close under the 
* Leaving out of consideration the horns of the carapace and the spinous 
process, the larve of the Cirripedes consequently agree closely, both in 
their external and internal structure, with the young forms of the Cyclo- 
pide, as these are made known to us by the admirable memoir of Claus 
(On the Anatomy and Shae Bingen History of the Copepoda, Wieg- 
mann’s Archiv, 1858, p. 1). This agreement shows itself not only in the 
similar number and analogous nature of the swimming feet, but also in the 
structure of the eye (see Claus, /. c. figs. 64 & 66), in the arrangement of 
the alimentary tube, and in the presence of a so-called oral hood (Mund- 
kappe), which is to be compared with the proboscidiform process. But the 
caudiform appendage of the Cirripede-larvee corresponds with the poste- 
rior segment of the Nauplius-form of the Copepod-larve, as will appear 
hereafter. 
+ Upon this period see the extremely accurate and complete description 
of Darwin (vol. 1i. pp. 110-123). 
