CERIANTHARIA. 



base, and here and there the mesogloea forms a little process towards either side. The musculature 

 is not developed. 



The cnido-glandular tract shews but little tendency to wavy coils, but encloses as a folded 

 tract a long process of the mesentery. The thick-walled nematocysts, which are not particularly 

 numerous have a length of 43 48^ and a breadth of i2/<. Smaller nematocysts (24 26/ji) occur as well. 



The craspedion regions (PI. 5, fig. 10) are well developed, long on protomesenteries 2 and the 

 metamesenteries of the ist and and cycles. On protomesenteries 3 and the other metamesenteries 

 they are less developed, which is connected with the fact that these mesenteries below the cnido- 

 glandular tract are considerably smaller and shorter than the first-named mesenteries. The homo- 

 geneous gland cells are numerous, the nematocysts sparse. 



The botrucnids (PI. 4, fig. 6) are well developed. Each botrucnid grain, cnidorage, (fig. 7, 8, PI. 4) 

 is ball or egg shaped and jointed to the mesentery by a shorter stem. The mesogloea of the mesen- 

 tery ramifies like the branches of a tree, of which one branch goes to each botrucnid grain. The 

 mesogloea enters the stem of the grain like a thread and broadens out at the base of the grain in 

 cup-like form. For the mesogloea seems to expand a little way at least up the periphery of the 

 grain, thus forming a shallow, more rarely a deep cup. Here and there it looks as though there were 

 a prolongation of the mesogloea edge in threads entering more deeply into the grain. The epithelium 

 on the sides of the cup as also on the stem is very thin; in the cup however, besides supporting cells 

 and an occasional mucus cell, are very large thick-walled nematocysts (length 43 48^ breadth 12 ft) 

 and also spirocysts (4^) in large numbers in the periphery. 



The botrucnidae are consequently not, as v. Beneden says (1908 p. 32), simply epithelial in 

 character; on the contrary they have like the filament a ground work of mesogloea, that even forms 

 a more or less clear cup-like structure. They are presumably ectodermal formations, and looked at 

 as a differentiation of the filament, they are probably homologous with the "acontia" - views which 

 I have developed in detail below in the 4th section, and which are in conflict with v. Ben e den's, 

 who regards the botrucnidae as endodermal formations. On the other hand it is possible that a part 

 of the loosened cnidorages consists only of epithelium, as v. Beneden states. In such a case a loos- 

 ening, probably disruption of the grain would have taken place just outside the mesogloea. See 

 further section 4. 



The mesenterial muscles are feebly developed, but shew no variation in arrangement from the 

 other Ceriantharia which I have described. The species is hermaphrodite. 



Larval forms. 



Arachnactis albida M. Sars 

 PI. 4, Fig. 1-3, PI. 5, fig. 7-8. 



For diagnosis and literature concerning this form and other northern Cerianthid larval forms 

 see Carlgren: Actinieu larven, Nordisches Plankton 1906. 



