6 
THE VOYAGE OF H.M.S. CHALLENGER. 
studied in a sagittal section as figured, the compound eyes — which, according to Darwin, 
are attached to the basal joints of the antennae — are visible. 
The structure of the interior of the body can easily be made out by the aid of the 
figure. M. is the mouth; it is surrounded by darkly pigmented parts, the exact shape of 
which is not very distinct ; the mouth gives entrance to the oesophagus ( (E) ; the latter 
has a horizontal direction, is furnished with a pair of coeca ( C ), and leads into a very 
capacious stomach (/S), from which a narrow intestine {Int. ) is seen to start. (Esophagus, 
coeca, stomach, and intestine are all very darkly pigmented. The six pairs of cirri and 
the caudal appendages present nothing particularly interesting ; the different cirri have 
only to shed their skin to change into the cirri of the Lepas ; the caudal appendages will 
have to undergo a very marked retrogressive metamorphosis to change into the 
rudimentary, uniarticulate, and smooth appendages of the full-grown Lepas australis. The 
nervous system is already quite distinctly visible ; it consists of the supraoesophageal 
ganglion (GS), and the six thoracic ganglia (G I.-G VI.). The first is situated very close 
to the coeca of the oesophagus and has a simple eye ( e ), represented by a small triangular 
spot of pigment attached to it (fig. 2, e). The chain of thoracic ganglia is on the right 
hand side of the stomach, between this organ and the ventral wall of what is properly 
the body. The ganglia are not yet separated by commissures, but are placed close to one 
another ; the first has an oval shape, and is much larger than the following ones The 
ganglionic cells which cover the surface of the different ganglia are extremely small. 
In the peduncular part of the body nearly all the room is filled up by a mass of con- 
nective tissue with very large meshes ; between this mass of reticular connective tissue 
and the layer of cells which represents the mantle a double layer of muscular fibres may 
be discerned. The fibres of the two layers are at right angles to each other, and both 
layers run parallel to the surface of the body and the valves of the Cypris ; in the figure, 
one of these layers is represented by the lines running parallel to each other, and also to 
the curved frontal line of the larva. This layer is composed of rather broad fibres (each 
fibre has an oval, not very elongate nucleus) and a breadth of 0 '01 2 mm., which will develop 
into the layer of longitudinal muscles of the peduncle of the Lepas. The other layer 
is situated between the former and the mantle, and shows much narrower fibres, with very 
narrow and elongate nuclei (each fibre has a breadth of only 0'003 mm.) ; this latter 
layer forms the circular muscular layer of the peduncle in the full-grown Lepas. The 
cells which constitute the mantle are relatively small, and are furnished with large nuclei 
(0'01 mm.) ; at different places they are richly pigmented. 
Between the fibres and nuclei of the connective tissue numerous fatty bodies are 
visible which are more like vesicles than grains ; they have an elongate shape, arc 
pointed at both extremities, and belong to what still remains of the yolk. 
The cell-masses which Claus 1 describes as the cement-glands were very strongly 
1 Claus, C., Untersuchungen zur Erforschung der genealogischen Grundlage, &c., Wien, 1876, p. 87. 
