CERIANTHARIA. 



63 



mesogloeal lamella, which forms a contimiatiou of the mesogloea that connects the ridges of the 

 stomatodaeum. The ciliated region of the side and bottom portions which pass continuonsly one into 

 the other without break thus forms a ciliated groove. This is well marked for the most part and 

 always in the oral portions of the ciliated tract (for example in protomesenteries 2 and the meta- 

 mesenteries in C. moubranacctis) throughout the whole course of the ciliated region, more rarely, as 

 in Arachiianfluis oligopodus on the proximal portions of protomesenteries 2 and the metamesenteries 

 of the first and second cycles, it disappears through a reduction in the number of t!ie ciHated cells 

 and is indicated only by a feeble ciliated streak, though that too very soon disapjicars and blends 

 with the craspedion region. 



The part of the ciliated tract adjoining the endoderm of the mesenteries is supported by a 

 mesogloeal lamella, which in A. lobiancoi. alhidn, Arachnantlms uligopodim and sarsi issues from the 

 median streak's mesogloeal lamella (Type i), but in the others from the undivided mesogloeal lamella 

 of the mesentery!) (Type 2) — a characteristic difference probably connected with the fact that in the 

 first named species the grooves of the ciliated tract are very shallow whilst in the others they are 

 considerably deeper. 



The ciliated tract region of the filaments, as several investigators already have repeatedly 

 remarked, is developed on all mesenteries, if the mesenteries are old enough to have acquired fila- 

 ment at all. An exception is found however in the directive mesenteries, which mostly lack a 

 differentiated ciliated region; only in species with well developed hyposulcns (in Arachnactis lobiancoi, 

 albida a.nd Arachnanihns and also in many of van Ben ed en's Ceriantharia larval forms) is a distinct 

 ciliated tract region found on the free border of the hyposulcus, but this filament region is made up 

 of half only of a filament, in as much as only one spirocyst-glandular tract ^) with the ciliated tract 

 going with it is develojied, as may easily be seen by comparing this part with the ciliated tracts on 

 another mesentery, for example, of ^Iraclniactis lobiancoi. This circumstance singular at first sight is 

 easily explained however, if with van Beneden we regard the hemisulci together with the hypo- 

 sulcus as homologous with the mesenterial filaments on the other mesenteries. For on the side facing the 

 directive chamber, the Inposulcus is common to both directive mesenteries and is not divided between 

 them separatel)-, and consequent!}- there cannot be in this case a distinct ciliated tract region for each 

 mesenter\', and on the continuation of the hyposulcu.s, the hemisulci, no differentiations of the ciliated 

 tract are found on the same side facing the directive chamber. Thus it is only the half of the filaments 

 remote from the directive chamber that may sometimes (in the species mentioned) be differentiated 

 on the directive mesenteries, whilst the parts lying towards the directive chamber have not divided 

 into distinct filament parts different for each directive mesentery. 



The ciliated tract region of the filaments is straight for the most part as in A. oligopodus, 

 C. lloydii, P. solifarins, and the most oral parts in C. incvibrauacciis. Sometimes even in these cases 

 it ma>- be folded, but possibl}- except in P. solitariits this may be due exclusively to a strong con- 



■) To this group also plainly belong, according to M c. Murrich's invesligalioiis, Pachyccrianthusfintlriatus and Ceri- 

 anthropsis americamis. I can corroborate this statement with regard to the latter. 



2) The second spirocyst-glandular portion and the ciliated groove running between the two divisions of the median 

 streak are indicated in A. lobiancoi and Arachiianthns oligopotins. 



