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 ,vthe mouth gives entrance to the oesophagus {(E). ; the latter 

 has a horizontal direction, is furnished with a pair of coeca ((7), and leads into a very 

 capacious stomach {S), from which a narrow intestine {Int.) is seen to start. OEsophagus, 

 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 supracesophageal, 

 ganglion {GS), and the six thoracic gangha {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 difierent 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 Cyj^ris ; 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 nuclei) and a breadth of 0-012 mm., which will develop 

 into the layer of longitudinal muscles of the peduncle of the Lepas. The other layer 

 is situcited 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 fuU-grown Lepas. The 

 cells which constitute the mantle are relatively small and are furnished with large nuc.ei 

 (O'Ol 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 Hke vesicles than grains ; they have an elongate shape, are 

 pointed at both extremities, and belong to what still remains of the yolk. 



The cell-masses which Claus^ describes as the cement-glands were very strongly 



1 Clans, C, Die genealogiscke Grundlage, &c., Wien, 1876, p. 87. 



