CERIANTHARIA. 



of the directive mesenteries is turned away from the directive couple, named dorsal but turned towards 

 the ventral directives. If then we find the orientation of the Ceriantharia from the mesenterial muscula- 

 ture (see above, mesenterial musculature) everything tells in favour of the view that the directive 

 mesenteries of the Cerianthidae --as I have already urged (1893) -- are dorsal directives and that 

 the siphonoglyph is a dorsal siphonoglyph, in other words, a sulculus. If on the other hand we 

 suppose the siphonoglyph here to be a sulcus, the disposition of the musculature of the non-directive 

 mesenteries would prove to be quite the reverse of that of all the other Anthozoa. 



Granted that the arrangement of the musculature is distinctly in favour of the view which 

 I defend, the case is not so clear at first sight with the arguments from embryology. It is well 

 known that different investigators such as Me. Murrich, Boveri, and in recent years Kingsley 1 ) 

 (1904, p. 349 351) have endeavoured to determine the homology of the mesenteries in the different 

 groups of Anthozoa by the order in which they first appear. That is, by examination of various but 

 usually only isolated stages of development, and very largely by means of the order in which the 

 filaments appear, they have believed they could prove, that the appearance of the first 8 mesenteries 

 in Actiniaria (Hexactiniae) and Madreporaria follows a fixed rule. Me. Murrich (1891) also, from the 

 difference in size of the mesenteries in a Ceriantharian larval form, Arachnactis, in the 8-mesentery 

 stage, drew the conclusion that the first 8 mesenteries in Ceriantharia, Actiniaria and Madreporaria 

 alike were developed in the same order and that the first 8 mesenteries occupy the same position in 

 all three groups, if the orientation of Ceriantharia is such that the siphonoglyph answers to the ventral 

 siphonoglyph of the other two groups. This view seemed soon after to gain confirmation, when van 

 Beneden (1891) shewed in a series of stages of development of Arachnactis, that the development 

 of the first 8 mesenteries in this larval form took place in the same order as in Actiniaria as a 

 rule, though some differences in the first formation of the chambers (loges) could be shewn to occur, 

 differences conditioned in part by the form of the stomatodaeum in the earliest stages. According to 

 this then, if we were to base the orientation of the body on the order of appearance of the first 8 

 mesenteries, the directive mesenteries of Ceriantharia would be ventral. 



But more recent and thorough investigators of the development of Actiniaria can lend Me. 

 Murrich and Boveri's views no stronger support than the discovery of a great variability in the 

 order of appearance of the earliest mesenteries in this group. Even earlier some investigators (L,acaze- 

 Duthiers 1872 and Wilson 1888) had pointed out various irregularities in the development of the 

 mesenteries, such as the occurrence of mesenteries 2 in the place where mesenteries 4 should appear 

 and more recently Gotte (1897) Appellof (1900) and Faurot (1903) have met with so many irre- 

 gularities in the development of the first 8 mesenteries in this gronp, that it is impossible, now-a-days 

 at least, to set up a fixed rule for the order in which the first 8 mesenteries appear. 



As it is very probable that the mode of life may have an influence on the course of develop- 

 ment of the mesenteries -- in crawling forms, as is well known, mesenteries are often suppressed in 



') Kingsley remarks that Halcampa has only one siphonoglyph. As I had previously (Zool. Anzeiger Bd. 27, 1904 

 P- 53 6 ) pointed out, the larval form described by H addon as belonging to the genus Halcampa is nothing of the sort 

 but a Peachia. It is likewise misleading to state that Cerianthus has a second siphonoglyph in the multiplication zone 

 (Kingsley p. 348). 



