﻿Note on Primnoa reseda /ro??i Fceroe Channel. 71 



is viviparous. Another form must therefore be added to the 

 growing list of Alcyonarians in which viviparity has been 

 demonstrated (see Thomson and Henderson in the list of 

 Eeferenees). 



Many of the polyps in the fragments at my disposal were 

 found to be crowded with embryos, but most of them were 

 unfortunately at the same stage of development. As we 

 have very few data in regard to the development of Alcyon- 

 arians, except the memoirs of G. von Koch, Wilson, 

 Kowalevsky and Marion, and Lacaze-Duthiers, the following 

 notes may be of service. 



Attached to the mesenteric bands there were elongated 

 clusters of ova at different stages of ripeness. Some of these 

 were seen to have a very definite envelope, from which a 

 stalk ran to the mesentery. Other larger egg-like bodies 

 were lying freely in the coeleuteron. An examination of 

 these showed that they were already well advanced in 

 development, that they were, in fact, diploblastic embryos. 

 Most were spherical or slightly ovoid, and some showed an 

 invagination at one pole. A few were solid, ihost showed a 

 well-developed coelenteron. The following measurements 

 of the diameter or of the longer axis were taken : — 0*4, 0'5, 0*6, 

 0"7, 0"8 mm. In many cases the wall was about 0"1 mm. in 

 thickness, of which about four-fifths was due to the inner layer. 



The ectoderm consisted of a single layer of columnar cells, 

 sometimes with large vacuoles ; the endoderm consisted of a 

 dense mass of small cells, in the middle of which there was 

 usually a large coelenteron. In most of the sections the 

 endoderm appeared like a syncytium, and about half a dozen 

 nuclei lay on every radial line across the wall one chose to 

 follow. A very distinct double -contoured middle-lamella or 

 mesogloeal plate lay, like a double basal membrane, between 

 the ectoderm and the endoderm. 



It seems, therefore, that we have to do with planulse, very 

 clearly differentiated into two layers, the inner of which is 

 several cells thick. It is probable that the 'coelenteron is 

 formed by histolysis in the middle of the endodermic mass. 

 There was no trace of typical gastrulse. It is likely that the 

 invagination or dimple seen in many cases at one pole is the 



