Hyatt.] 110 [March 5, 



the oesophagus was taking place, and suggests that a canal 

 existed in the fore part of the animal into which this opened 

 and which has been obliterated (Balfour) ; otherwise it is hard to 

 give a reason for the absence of an anterior connection with the 

 mesenteron. Dohrn seems to be sustained in his idea that the 

 ectodermal invaginations are due to their former existence as 

 parts of tubes which communicated with the interior ; and this 

 idea, though we were not aware of the fact previous to the 

 writing of this page, is in large part parallel to that which we 

 have applied to the explanation of the origin of the stomodea 

 and the proctodea in the Invertebrata. Though too slightly 

 acquainted with the embryology of vertebrates to venture a 

 decided opinion, we can, in view of the extraordinary clearness of 

 the evidence, suggest that these views and those of most writers 

 are reconcilable on the basis of Dr. E. B. Wilson's late research 

 upon the Actinozoa. 



Prof. Sedgwick's theory has been supported by Dr. E. B. Wil- 

 son (Mitt. d. Zool. Stat. Neapel, vol. vn, p. 23), who goes a step 

 farther and homologizes the cavity formed by the mesenterial 

 filaments of the Actinozoa when feeding with the mesenteron of 

 the embryos of Peripatus and Amphioxus. According to Wilson 

 the mesenterial filaments or inner edges of the lower parts 

 of the fleshy septa in the Actinaria and the six ventral filaments 

 of Alcyonaria are laterally expanded and consist of feeding 

 cells different from the smaller epithelial cells of the septal 

 chambers. The large cells of the filaments are elongated and 

 capable of intracellular digestion, and the smaller cells of the 

 intermediate chambers never have inclusions, and are unsuitable 

 for the performance of this function. While in the act of feeding 

 the endodermic filaments, or those parts of them which are com- 

 posed of endodermic cells, spread themselves out around the food 

 mass and actually in some cases form a union, thus construct- 

 ing a temporary mesenteron in which, however, intracellular 

 digestion alone takes place. According to Wilson the dorsal fil- 

 aments of Alcyonaria and the upper parts of those of Actin- 

 aria are derived from prolongations of the ectoderm of the 

 actinostome and these aie circulatory in function, and not to be 

 confounded with the endodermic parts which are digestive. We 

 have never been able to understand the validity of the objections 



