CERIANTHARIA. 



diminution in the length of the qiiartettes no doubt takes place, but this diminution is not regular 

 as I have shewn in another paper (1912): here and there a break occurs, so that a quartette lying 

 nearer the directive chamber may be less developed than one situated further away. Thus the fifth 

 quartette is considerably longer than the fourth and provided with longer ciliated tracts, the yth 

 longer than the 6th. The gth longer than the 8th. An indication that a similar relation also exists 

 between the 2nd and ist quartettes, appears from the fact that the metamesenteries of the 3rd cycle, 

 in the 2nd quartette at least, are at least as long as and provided with longer ciliated tracts than the 

 corresponding mesenteries in the first quartette. So great a departure 1 ) as this of C. mcrnbranaccus 

 from the normal decrease in length of these mesenteries as they approach the multiplication chamber, 

 I have not discovered in any other Ceriaiithariutn, although in several species (C. lloydii, P. multipli- 

 catus, solitarius, Bolrucnidifer norvcgius) the mesenteries of the third cycle in the second quartettes 

 are better developed than the corresponding mesenteries in the first. That here the same relation 

 is not met with in the case of the metameseuteries of the 6th, ;th and 8th quartettes is doubtless 

 connected with the fact that several of the above species have a smaller number of mesenteries, and 

 perhaps also with the fact that, as in P. multiplicatus for example, so little difference is found between 

 the mesenteries in the first and second, or the third and fourth quartettes. In several species too 

 such as C. valdiviae the arrangement of the mesenteries in quartettes is not clearly marked. Since 

 this arrangement in quartettes is so indistinct in many species, it is quite probable that it is a later 

 acquisition of the Ceriantharia and not an original character. Of like import too is the circumstance 

 that the tentacle cycles and the mesenteries in younger individuals have a simpler arrangement than 

 in the fully grown. In such circumstances the quartette arrangement would not prove to have any 

 significance for the ascertainment of the affinities of Ceriantharia with other Anthozoa (see Fan rot's 

 paper 1891 p. 66 which compares the quartette arrangement in Ceriantharia with the arrangement of 

 septa in Rugosa). 



A peculiar arrangement of the mesenteries in Ccrianthcopsis americanus has been described 

 by Me. Murrich (1910) the results of whose researches I can confirm. (For some minor diver- 

 gencies from Me. Mur rich's account I refer to the description of the species p. 24). It is not merely 

 that the metamesenteries in every quartette have a different arrangement from the normal in Cerian- 

 tharia, since in every quartette we find first a mesentery of the 2nd cycle (m) followed by one of the 

 third (B) then one of the first (M) and lastly one of the 4th (bj but the metamesenteries of the 

 first cycle increase in length towards the multiplication chamber though with several breaks as in 

 C. membranaceus. The other cycles of mesenteries up to the fourth inclusive on the contrary diminish 

 as they near the multiplication chamber, with the possible exception of the second cycle. 



Finally we must mention a third kind of quartette arrangement based on Torrey and Klee- 

 berger's figure of Botruanthiis benedeni. Here in each quartette the metamesenteries occur in the 

 following order. In the first place a mesentery of the first cycle, next one of the fourth, then one of 

 the second, and lastly one of the third cycle. That is, the mesenteries of the third and fourth cycles 

 have changed places, so to speak, provided that Torrey and Kleeberger's observations are correct. 



l ) According to Torrey and Kleeberger's figure of C. johnsoni a similar break appears to take place at the 

 third quartette in this species also, and Me. Murrich's figure of Pachycerianthus fimbriatus shews that a break occurs at the 

 7th quartette. 



