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an other obstacle is that the pair of mesenteries, which is formed first with the Hexactiniae and 
which dominates the following development, would be represented by the second pair of anterior 
secondary mesenteries of Leiopathes and so would be absent in all the other Antipatharia. 
\ an Beneden can not see any regression in the secondary mesenteries, since the Edwardsiae 
demonstrate that, with Hexactiniae, the tentacles disappear after the interseptal chambers. None 
ot the Antipatharia has more than six tentacles, and so the secondary mesenteries are new 
ones. Besides van BeNeden is of opinion that Brook would have found it extremely difficult to 
prove that, with the so very divergent genera of the Antipatharia, the regression of the mesen¬ 
teries should be advanced everywhere to the same stage, except for Leiopathes and Cladopathes. 
The opinion about the primitive state of the Antipatharia should be kept separate from 
van Beneden’s thesis, that the Antipatharia ought to be combined with the Ceriantharia to the 
Ceriantipatharia, in contrast with the remaining Hexactiniae. — The following characters of 
the Antipatharia are put together by him as of general value: six primary mesenteries, two 
of which are transversally directed and fertile, and four of which are directives; six tentacles 
which are situated above the primary interseptal chambers: two median and four lateral, the 
latter ot which are equal two and two ; bilateral symmetrical polyp; sulcus and hyposulcus ; 
ectodermal longitudinal musclefibres in the bodywall. According to van Beneden these characters 
are very like those of the Arachnactis- larva, which he named Cerinula; for this reason he- 
regards the Antipatharia as sexual forms, which morphologically appertain to the larval stage 
of Cerianthus. The Cerianthidae have originated from ancestral forms, which are like the present 
Antipatharia and which now are represented by the larva Cerinula and by the genus Clado¬ 
pathes. The Antipatharia have become inclined towards an increasing number of mesenteries 
through a partition of the lateral interseptal chambers, while with the Ceriantharia the new 
e _teries take origin in the posterior median interseptal chamber of the larva. Against this 
opinion may be said that the transversal primary mesenteries are not the only ones which may 
be fertile; besides the lateral tentacles are in most cases not equal two and two in the sense 
of van Beneden, for usually the distal pair of lateral tentacles is smaller than the proximal 
lateral pair, so that the polyp is not exactly bi]aterally symmetrical. The difference in length 
between the anterior and posterior pair of lateral tentacles, as van Beneden has found it in 
young polyps, I have seen nowhere, neither in young polyps, nor in adult ones. Also the 
existence of a true sulcus and hyposulcus I am very much inclined to doubt. At last: the 
situation of the longitudinal musclefibres on the mesenteries is very different from those of the 
Ceriantharia, while the succession in the origin of the mesenteries in Antipatharia can only be 
supposed by van Beneden theoretically since all ontogenetic data are entirely lacking. 
Goette (8) is of the same opinion as van Beneden; he sees the Antipatharia as primi¬ 
tive forms, and he combines them with the Ceriantharia; both are deduced from a Scyphopolyp 
with six mesenteries. Goette deviates from van Beneden in questions of descendency, which 
na\ e nothing to do with the relationship between the Antipatharia and the Ceriantharia. 
Delage and H£rouard x ) neither believe the twelve mesenteries of Leiopathes to be a 
1) Traite de Zoologie concrete. Tome II. 
