DROMALIA ALEXANDRI. 305 



transverse, on which the cell layers could be traced, though in places they are 

 damaged or obscured. In its essentials the aurophore agrees with the account 

 of it given by Lens and Van Riemsdijk for Archangelopsis. As in that genus, 

 it is nothing more than an evaginated portion of the pneumatophore; and all 

 the cell layers of the latter can be traced through it.^ Its outer wall, consisting 

 of ectoderm, supporting layer, and entoderm, is continuous with the pneumato- 

 codon. The inner wall, composed of the same three layers, is the continuation 

 of the pneumatosaccus; its entoderm, of course, faces that of the pneumato- 

 codon. The peculiar structure called by Haeckel the "pistillum" is exactly 

 comparable to the pneumatochone, or "aii- funnel " of Physophora, as Lens and 

 Van Riemsdijk have shown. But the secondary ectoderm here reaches a much 

 higher state of development than in that genus. 



Although this general account is true both for Dromalia and for Archange- 

 lopsis, radial sections thi-ough the aurophore of the two genera show very 

 different appearances, due to the excessive development of the pneumatochone 

 in Dromalia. Wliile this is conical and connected with the pneumatosaccus 

 by a narrow neck in Archangelopsis, in Dromalia it is cjdindrical, about five 

 times as long as broad. Furthermore the chitinous ring, developed from the 

 ectoderm-lining of the pneumatosaccus, is so much more highly developed 

 in Dromalia that it forms a thick-walled cylinder which, except at its distal 

 extremity, entirely separates the primary ectoderm from the secondary ectoderm 

 filling its lumen (Plate 24, fig. 6, 8). As in Archangelopsis a shining chitinous 

 layer continuous with this tube lines the entire inner surface of the pneumato- 

 saccus except in the immediate neighborhood of the pneumatochone, where it 

 is overlaid by a disc-like expansion of the secondary ectoderm. In one speci- 

 men of .Archangelopsis Lens and Van Riemsdijk found the secondary ectoderm 

 lining the entire pneumatosaccus, but this is not the case in any of the "Albatross" 

 examples of Dromalia. The portion of the secondary ectoderm which lies within 

 the chitinous cylinder encloses numerous spherical cavities explained, and proba- 

 bly correctly, by Lens and Van Riemsdijk (:08), as formed by the gas secreting 

 cells. Likewise in the region where the primary and secondary ectoderm merge 

 into each other, there are traces of giant amoeboid cells, such as have been 

 described by previous authors in other Siphonophores. In Archangelopsis 

 these cells are very prominent (Lens and Van Riemsdijk, :08, p. 95). To com- 

 plete the account of the pneumatochone I need only mention that the chitinous 

 cylinder is of a distinctly fibrous nature. 



' The nomenclature used is that of Lens and Van Riemsdijk. The pneumatophore consists of an 

 outer wall " pneumatocodon " (Luftschirm), and an interior sac, the "pneumatosaccus" (Luftsac). 



