The mesenterial Filaments of the Alcyonaria. 25 



divisions sliould become morpliologically"^as well as physiologically dis- 

 tinct by a longitudinal Splitting of tbe oesopbagus , accompanied by a 

 Fusion of tbe meseuterial filaments, we sbould have an animai witb 

 stoniodaeum and proctodaeum , a closed mesenteron , and paired meso- 

 blastic somites. — Assuming for tbe moment tbe probability of sucb a 

 view, we may ask wbetber we can find any indications wbicb division of 

 tbe oesopbagus is to be regarded as tbe anterior one — tbat is as tbe 

 stomodaeum. In tbe Alcyonaria no sucb indications exist, on account of 

 tbe grcat abbreviation in tbe developraeut, but in tbe Cerianthidae we 

 may possibly find tbe iiey to tbe problem. In tbis group a ciliated groove 

 exists , as in Alcyonaria , and according to tbe Hertwigs is situated 

 upon tbe same side of tbe oesopbagus, tbat is, tbe ventral. Tbe 

 principal septa decrease regularly in size from tbe ventral to tbe dorsal 

 side, and the Hertwigs conclude tbat tbis represents tbe order of tbeir 

 developinent in tbe erabryo. In otber words , tbe dorsal cbambers are 

 tbe youngest , like tbe posterior somites of Annelides or Arthropods. 

 Hence, according to tbe view bere suggested, tbe ventral division of 

 tbe oesopbagus would represent the stomodaeum, and tbe dorsal division 

 the proctodaeum. — Tbis view, if it sbould be shown to be well-founded, 

 would involve a completely new couception of tbe structure of a polyp- 

 Tbe so-called oesopbagus would represent the uuited stomodaeum and 

 proctodaeum of higher animals, and tbe so-called anal pore of Cerianthns 

 would not be in any way morphologically comparable witb an anus. Tbe 

 so-called dorsal and ventral surfaces would be respectively tbe poste- 

 rior and anterior extremities , tbe oral face would be ventral , and tbe 

 base or aboral extremity dorsal. The radial Chambers and i)osterior 

 part of the stomach would represent tbe coelom, and tbe space between 

 tbe mesenterial filaments would correspond witb the cavity of the me- 

 senteron. 



It is perhaps hardly necessary to add tbat tbis coraparison was 

 first suggested to me by Balfour's remarkable observations upon tbe 

 development of Peripatus (edited by Moseley and Sedgwick) and tbat 

 it aceords fully witb bis conception of tbe transition from radiate to bila- 

 teral animals. Tbe comparison of tbe radial cbambers of polyps witb 

 tbe somites of Peripatus has, so far as I know, never been published. 

 It was however suggested by Mr. Adam Sedgwick in an oral communi- 

 cation to tbe ßoyal Society, in Dee. Ib82, and at tbe sanie time be called 

 attention to tbe possible significance of tbe ventral groove of tbe Oeso- 

 phagus (in Peachia) . To him therefore belongs wbatever credit may 

 attach to the origination of tbis comparison. 



