The mesenterial Filaments of the Alcyonaria. 23 



regiou of degenerated ectoderm cells marked in. in fig. 1 1 , represents 

 the original ectoderniic part of the ventral filamenti but this is un- 

 certain. 



V. The relations of the Anthozoa to the Enterocoela. 



The fact that the digestive functions are confined to the mesenterial 

 filaments suggests certain comparisons between the Anthozoa and the 

 higher animals to which I wish to call attention, not by v^ay of setting 

 up a completely formulated theory, but only as a Suggestion for farther 

 investigation of the facts. 



If we consider the entodermic filaments or their repräsentatives 

 physiologically, v^^e must regard them as the representatives of the ali- 

 mentary canal of higher animals, and I would suggest that they are not 

 only physiologically but also morphologically the equivaleuts of the 

 enteron of Enterocoela. If we imagine the filaments to fuse together by 

 their edges and lower extremities , we should have a digestive tube, 

 surrounded by closed cavities in the walls of which are developed the 

 muscles. During digestion, as I showed in the case of Leptogorgia^ the 

 filaments are closely approximated around the mass of food, so that 

 when in this condition they practically form a tube. And I have ob- 

 served in two dififerent genera that the filaments do sometimes 

 actually fu se together, as shown for instance in Alcgonium, fig. 3, 

 at v.l. f. 



If this be so, then the radial Chambers of an Anthozoan correspond 

 with the mesodermic diverticula of Enterocoela^ a view which has al- 

 ready been more or less distinctly enunciated by several writers. Morpho- 

 logically we may regard the radial Chambers as diverticula from the 

 primitive enteron. If we compare in Alcyonaria the histological sti'uc- 

 ture of the walls of these Chambers with that of the entodermic fila- 

 ments, we find that the difiference is exactly comparable with the differ- 

 ence between the mesodermic diverticula of Sagitta or Amphioxus and 

 the walls of the enteron. The cells of the radial Chambers, like those 

 of the mesodermic diverticula , give rise to the muscular system , and 

 according to the same type of histological differentiation ; whereas the 

 cells of the filaments , like those of the enteron , become specialised for 

 the performance of the digestive functions. If the radial Chambers be- 

 came closed by the union of the mesenterial filaments , no-one would 

 hesitate, either upon embryological, histological or physiological grounds, 



