38 
THE VOYAGE OF H.M.S. CHALLENGER. 
V. THE EYE OF LEPAS. 
I believe Leidy was the first who observed in an adult Cirriped an organ of vision. 1 
In Balanus there are, according to him (and Darwin has confirmed the correctness of 
his observation), two small eyes which stand apart from each other laterally and, owing 
to this discovery of the American naturalist, Darwin 2 was led to look for them in 
Lepadidse. In Lepas fascicularis he found an elongated almost black eye composed 
of two eyes united together. The eye is innervated by two nerve-cords which extend 
from the front of the two supraoesophageal ganglia, and which before reaching the eye 
run into two small, perfectly distinct, oval ganglia. From the opposite ends of these 
two ganglia smaller nerves run, and, bending in at right angles, enter the elongated eye 
beyond the middle. 
I do not think that any description of this organ has been published since Darwin’s. 
I made preparations of it in Lepas anatifera and in Lepas fascicularis. The place it 
occupies in the first species may be seen on Plate VI. figs. 7 and 8. On removing 
the ligament between the two scuta as well as the muscles which are here placed between 
this ligament and the widened stomach, the surface of the latter with its black (hepatic ?) 
excrescences and the white pancreatic glands appear. At a distance of about 6 mm. 
from the supraoesophageal ganglion in an adult Lepas anatifera, a small oval black spot 
is seen attached by means of connective tissue to the surface of the stomach. This is 
the eye. Morphologically it represents the small pigment spot which, in the Cypris- 
larva (PI. II. fig. 2, e), is attached to the upper surface of the supraoesophageal ganglion, 
and which is the remainder of the simple eye of the Nauplius -larva. In an adult 
Lepas anatifera it measures 0'25 mm. only in length, its breadth being not quite 0T5 
mm. I believe its function to be of no consequence, in Lepas at least, for I do not 
understand how a ray of light can ever reach it, but the little organ beautifully illustrates 
the persistence of an old larval structure. 
Most curious, however, is the fact that this rudimentary organ is indeed furnished 
with a kind of special ganglia (PI. VI. fig. 9). Between the two broad (antennal) 
peduncular nerves, four thinner ones separate from the supraoesophageal ganglion. Their 
thickness is not quite the same ; the two outer ones are slightly stronger than the other two 
which lie very close to one another, almost exactly midway between the two other 
nerves. These four nerves can be traced up to a very short distance (about 0'6 mm.) 
from the small eye. Here the two stronger nerves of the four bend slightly outwards 
so as to approach a little more nearly to the peduncular nerves and show a distinct 
swelling, in the interior of which two elongate ganglionic cells are to be observed. I 
1 Leidy, Proc. Acad. Nat. Sci. Philad., No. 1 , vol. iv., January 1848. 
2 Darwin, Lepadidte, 1851, p. 49. 
