2t4 THE- VOYAGE OF H.M.S. CHALLENGER. 



animals, and I then became certain that Darwin's descrij)tion was not correct in one 

 very important regard. The sack is not closed at the bottom, but gives entrance to the 

 body cavity of the animal. 



For want of material I have been obliged to limit my researches to the pedunculated 

 Cirripedia ; in the sessile Cirripedia, however, there cannot be the slightest doubt that the 

 apparatus will prove to have about the same structure ; the orifices are here never pro- 

 duced nor tubular.^ I got by far the best preparations from specimens of Scalpellum 

 vulgare, Leach, which I received from the Zoological Station at Naples. The figures on 

 PL v., as well as the description, are based upon preparations of these specimens. 



Fig. 1 of PI. V. shows a complete transverse section through the thorax of 

 Scalpellum vulgare a little below the first cirrus. The large cavities [A) separated in the 

 figure from one another by the band of connective tissue [B) represent parts of the body 

 cavity. An epithelial clothing (a true coelomic epithelium) cannot everywhere be made 

 out distinctly ; yet I think its presence may be safely concluded from the cellular 

 remains which here and there adhere to the connective tissue, in the shape of elongate 

 and rather flat nuclei. The section passes longitudinally through the long and flattened 

 tube which belongs to the right outer maxilla ; the duct on the interior is clothed by a 

 thin chitinous tunic, with a chitinogenous epithelium everywhere beneath it ; both the 

 chitinous tunic and its matrix are the continuation of the outer body-wall and are no 

 doubt true epiblastic products. Fig. 3 of PI. V. represents a longitudinal section of 

 one of the segmental organs. From the outer wall of the flattened tube thin transverse 

 fibres of connective tissue run towards the wall of the duct. Having passed longitu- 

 dinally through the tube, the duct may be traced for a short distance beneath the surface 

 of the body ; it then passes over into a very narrow channel which passes through a 

 compact mass of cells. The whole mass of cells has the shape of a bell ; the limits of 

 the difi"erent cells are not very distinct, but the diff"erent nuclei are. They are oval and 

 their longest diameter is about 0'005 mm. (fig. 2, PI. V.) The surface of the cells 

 borderino- the narrow channel is markedly protuberant, so as almost to meet that of the 

 opposed cells ; in very favourable sections only can the presence of the channel be made 

 out. To judge from the great number of nuclei, the cell-mass, at least on one side, ia 

 formed of more than a single layer. Whereas the cells of the duct have their nuclei with 

 their longer axis parallel to the surface of the wall of the duct, those of the bell-shaped 

 cell-mass are rather perpendicular to the surface of the very narrow channel. Moreover, the 

 latter are very characteristic on account of their staining much more intensely than do those 

 of the chitinogenous cells or of the surrounding connective tissue. Towards the inferior 

 of the body-cavity the thick cell-coating of the narrow channel slopes and soon terminates ; 

 from the body-cavity the entrance of the narrow channel is distinctly funnel-shaped. The 

 chitinous membrane which clothes the interior of the duct is not present at the surface of 



» Darwin, BalanidEe, 1854, p. 97. , 



