IO Edmund B. Wilson 



Comes eveu columnar, thoiigh never to the same exteut as in the Aeti- 

 nians. I am inclined to believe that this depencls to some exteut iipou 

 the state of contraction, and that when the polyps are fiiUy expanded 

 the epithelium is always comparatìvely thiu. So far as 1 have seen, no 

 gland-cells like those of the entodermic filaments are found in this 

 epithelium, and no evidence of intra-cellular digestiou can be disco v- 

 ered. Most of the cells composing the epithelium produce muscle- 

 fibres at their inner ends — that is, they are myoblasts — and I have 

 brought forward evidence (Development of li&mlla, I.e.) to show that 

 nearly or ali of the musculature of the Alcyonaria is entodermic. 



This histological diflferentiation in the entoderm I believe to be a 

 fact of great significance, as pointed out in part V. 



II. Development, structure aud functioii of the dorsal or 

 ectodermic filameuts. 



a) Development. 



I have already showu that in Renilla aud Leptogorgia the dorsal 

 filaments first appear as two slight prominences upon the dorsal lip 

 of the Oesophagus i, whence they grow backwards along the edges of 

 the dorsal septa until they reach the posterior end of the polyp (or in 

 Renilla the posterior end of the so-called polyp-cell) . The same is 

 true oi Clmularia, as shown in fig. 1. The dorsal filaments, one of 

 which is shov^i^n at d.f. , appear as two short prolongations from the lips 

 of the Oesophagus, and in later stages gradually extend downwards to 

 the bottom of the stomach-cavity, but without losing their connection 

 with the Oesophagus. If a longitudiual section he made through the 

 Oesophagus and these rudimentary filaments, the latter are found to be 

 simple continuations of the inner or ectodermic layer of the former. 

 Their cells agree exactly with those of the inner layer of the Oesophagus, 

 and there is not the slightest trace of a limit between them ; it is in 

 fact impossible to say where the filament begins. On the other band, 

 they dififer totally from the entoderm cells oftheseptum. The latter 

 are fiat and polygonal with large pale nearly round nuclei. The cells 

 of the filament and of the inner layer of the Oesophagus are of a high 

 columnar form and possess small ovai nuclei which stain very intensely. 

 The contrast between these two kinds of cells is most striking and 

 in properly prese ved specimens appears at the first glance. 



1 Phil. Traos. 18S3, figa. 117, 177. 



