12 Edmund B. Wilson 



meuts, and Kölliker has showu that these filaments correspond with 

 the dorsal pair of the sexual polyps. I bave examined the structure of 

 these filaments in the zooids of Pennahda, FunicuUna and Kophohelem- 

 non , and find that they agree entirely in structure with those of the 

 sexual polyps. Like the latter, the filaments of the zooids are 

 downgrowths from the stomodaeum and are therefore 

 ectodermic structures. Their cells are of a high columnar form 

 with small iutensely staining nuclei, and in longitudinal sections they 

 are fouud to be continuous with the dorsal ectoderm of the stomodaeum. 

 In fact, a longitudinal section through a zooid is absolutely indistinguish- 

 able from a corresponding section through a young sexual polyp before 

 the appearance of the entodermic filaments, and A and B, fig. 13, would 

 do equally well for figures of zooids , except for the rudimeut of an 

 entodermic filament in B. 



b) Structure. 



A comparison of the ectodermic filaments in various genera of 

 Akyonaria shows that they bave almost precisely the same structure 

 throughout the group. To illustrate this similarity I bave given figures, 

 drawn to the same scale with fig. 12, of trausverse sections of these 

 filaments in the sexual polyps of Gorgonia (fig. 6) , Paralcyonium (fig. 8), 

 a zooid of Kophohelemnon (fig. 9), and a young polyp of Funiculma 

 (fig. 7). A glance at these figures shows that the structure is essentially 

 the same in ali — though these genera represent three widely diflferent 

 families — and differs entirely from that of the entodermic filaments 

 (fig. 12). The filament consists of two entirely different portions. 

 Much the greater part consists of high columnar cells, each with a small 

 ovai iutensely stained nucleus and a single powerful cilium at the outer 

 end. The nucleus is usually situated in the middle or basai part of the 

 celi and seldom in the outer third ; so that in sections the outer part of 

 the filament appears clear, contrasting sharply with the inner two thirds 

 where the nuclei are closely packed together. These cells* are quite 

 similar to those of the inner layer of the Oesophagus, and obviously 

 represent the ectodermic downgrowth from the stomodaeum. 



The columnar cells are arranged so as to form a long solid band 

 on the edge of the septum, which I shall cali the ectodermic band. 

 As seen in sections, this band has a bilobed form — or in other words, 

 a longitudinal groove runs along its middle. The form of the groove 

 varies greatly according to the state of contraction. The most usuai 

 form is shown in fig. 7 [Funiculinà] , but the groove may be much more 



