REPORT ON THE DEEP-SEA MEDUSAE. lxxi 



radial canals, and four interradially between the latter (Pis. I. fig. 2, mi). The abaxial 

 wall of the cathammal fissures is formed by the thin cell layer of the dorsal endoderm 

 lamella, which lies on the concave inner surface of the notumbrella, whilst its axial wall 

 is formed by the supporting plate of the ccelumbrella, of which the ventral endoderm 

 lamella is lost. The septal cavities are remarkably developed, for example, in Codonium 

 and Sarsia among the Codonidae, in Tiara and Catablema among the Tiaridae, in Cytacis 

 and Rathkea among the Margebdae, &c. They have been hitherto erroneously regarded 

 as ccelome fissures, and placed along with the true body cavity (" cceloma") of the higher 

 animals. Such a cavity does not, however, exist in the Medusae any more than in other 

 urticating animals. The septal cavities of these Anthoniedusae rather arise from the two 

 fused cathammal plates between the eight principal radial Hnes becoming parted second- 

 arily, and only remaining fused in these eight lines. From this we see most clearly that 

 the cathammal plates pass continuously into the endoderm layer of the radial canals, where 

 these touch the lateral margins of the septal cavities. On the other hand, the cathammal 

 plates are completely separated from the ectoderm of the umbrella, externally by the 

 gelatinous body of the notumbrella, internally by the supporting plate and muscular 

 plate of the ccelumbrella. 



§ 104. Gastrovascular system of the Craspedotae and Acraspedae. The two sections 

 of the class Medusae show differentations, which are perfectly analogous, in the forma- 

 tion of their gastrovascular system, but still present, in spite of all similarity, a constant 

 and therefore very essential difference. In all the Acraspedae, movable gastral filaments 

 (" filamenta gastralia"), or "internal gastral tentacles," are found on definite places, 

 whilst these are never present in the Craspedotae. In the Acraspedae there are at least 

 four of these gastral filaments, which are regularly distributed interradially. They are, 

 however, generally very numerous (usually over a hundred, often over a thousand), and 

 arranged in such a manner as to form four interradial groups of filaments (" phaeelli "). 

 The movable filaments of these phaeelli are sometimes arrayed in a single row, some- 

 times in several rows ; they are sometimes simple, sometimes branched, and always 

 consist of a solid, cylindrical or band-shaped gelatinous filament (a process of the fulcrum) 

 covered with endodermal epithelium. The phaeelli of the Acraspedaa (or "Phacellotas") 

 are, therefore, of great phylogenetic importance, as indications of them already exist in 

 the polyp nurses of this section. The Scyphopolyps, from which the Acraspedae are 

 descended, have all four interradial gastral ridges or gastral taeniola on the inner 

 surface of the wall of the stomach, and from these the " filaments " of the " Scyphornedusae " 

 are developed. 



§ 105. Taeniola or gastral ridges (" taeniola gastralia, " ft). The phylogenetic hypo- 

 thesis (§ 6) that the two sections of the class Medusae have arisen independently of 

 one another from two different groups of polyps is fundamentally supported by the 

 fact that the important difference in their gastral formation mentioned above (their being 



