CKRIANTHARIA. 59 



of a single species only, A rachnactis bournci, has been closely studied by van Beneden. That is quite 

 true, yet if we draw a distinction between protomesenteries and metamesenteries (protocnemes and 

 deuterocnemes Me. Murrich) it seems to me the only possible course to draw the line dividing them 

 immediately after the 6-mesentery stage. There are other circumstances in favour of this besides the 

 appearance of a multiplication zone from this stage onward. For we must remember, that the fourth 

 couple of mesenteries (according to the series of development in the mesenteries maintained by Me. 

 Murrich) in Actiniaria, Madreporaria and Zoantharia is a couple of directive mesenteries, whilst in 

 Ceriantharia it is nothing of the sort. The obvious assumption is, that there has been a differentiation 

 of Ceriantharia from the other Anthozoa with the exception of Antipatharia previous to the 8-mesentery 

 stage. The likeness too of the young Cerianthid larval form to a primitive Antipatharian form, as 

 regards mesenteries, stomatodaeum, chambers and presence of an ectodermal musculature of the 

 column, though not at once decisive, is still very striking. 



In view of the facts above adduced I must give my adhesion to van Beneden's view that Ceri- 

 antharia have only 6 protomesenteries. Me. Murrich's contention that in this group 8 proto- 

 mesenteries would be found, based as it is solely on the order of sequence in the appearance of the 

 first 8 mesenteries, seems untenable for the simple reason, that the order in which the mesenteries in 

 Actiniaria 1 ) occur, is very inconstant 



6. The mesenterial filaments, acontia and botrucnidae. 



Although several investigators, above all A. von H eider (1879), the brothers Her twig (1879) 

 and in particular van Beneden (1898) have studied the free border of the mesenteries with its 

 appendages, several points of structure are not yet made clear both in the case of the mesenterial 

 filaments and of the so-called acontia and botrucnidae discovered by van Beneden. As I have had 

 for examination adult representatives of Cerianthidae both with "acontia" and with botrucnidae, as 

 well as specimens without "acontia" and botrucnidae, I state here my conception of these organs, 

 referring at the same time to my description of certain Cerianthidae in Mittheilungen aus der zoolo- 

 gischen Station zu Neapel 1912. Since I touch several times below on the different authors' views of 

 the mesenterial appendages, I take it to be unnecessary to give a chronological sketch of the history 

 of opinion on the supposed structure of these organs. 



To begin with the mesenterial filaments; it is already known, thanks to v. Heider and Hert- 

 wig, that at their commencement immediately below the stomatodaeum they consist of a middle 

 portion, a so-called cnido-glandular tract, and of 2 lateral portions, ciliated tracts, also that the cnido- 

 glandular tract is continued aborally in a wavy single portion, "la portion tenninale on simple, qui 

 se prolonge jusqu'a 1'extremite aborale du filament" (van Beneden 1898, p. 34), but as far as I can 



') Unfortunately the order of sequence of the mesenteries in Actiniaria and Madreporaria rests for the most part 

 only on observations of disconnected stages and not of complete sequences of development. Whilst Me. Murrich in his 

 work on the phytogeny of Antinozoa (1891) thinks that Ceriantharia pass through an Edwardsia stage, he does not affirm 

 this so distinctly in his recently published work (1910). There he urges merely that Ceriantharia pass through an 8-mesen- 

 tery stage which is common to the other Anthozoa with the possible exception of Antipatharia. Ceriantharia certainly pass 

 through an 8 10 12 mesentery stage and so on, but from grounds stated above it is very improbable that a larval form 

 with 8 mesenteries can be the primitive form for all Anthozoa with the exception of Antipatharia. 



8' 



