ANATOMY OF MUSSA AND ETJPHYLLIA. 25 



The tentacles were so completely retracted in my specimens 

 that I could not determine anything about them. In some 

 longitudinal sections there are infoldings on the surface of the 

 peristome, such as are represented in fig. 4, but I could not 

 say with any certainty whether these are tentacles or not. 

 The ectoderm lining the involutions does not differ from that 

 of the rest of the body surface. 



Histology. — This does not differ from the normal Actinian 

 type. The ectoderm is of the ordinary character, and contains 

 numerous nematocysts '002 mm. in length when inverted. 



The calicoblasts in most situations agree with the form 

 described in Fungia, and the majority of cases, namely, rounded 

 or polygonal, soft-looking granular cells, which do not stain 

 easily, possessing nuclei which stain but slightly in borax 

 carmine. They occur everywhere, in a scattered condition or 

 forming a distinct layer, between the mesoglcea and the corallum. 

 The calicoblasts which clothe the uppermost and peripheral parts 

 of the septa are of a different character, being drawn out into 

 very long, narrow, columnar cells, just like those described by 

 Fowler for Lophohelia ; and it will be observed that they cor- 

 respond very closely in position to the similar cells in that form. 

 In both cases they are found at the seat of the greatest activity 

 of coral secretion. In several of my preparations I found 

 pyramidal or oval cells exhibiting a longitudinal or radial 

 striation, which exactly resemble those drawn by Sclater for 

 Stephanotrochus and von Heider for Astroides, and described 

 by them as calicoblasts. I have no hesitation in saying that in 

 Mussa they are not calicoblasts, since they differ entirely from 

 the cells above described, which from their position are undoubt- 

 edly calicoblasts, and they are never found in the regions of 

 coral secretion. On the contrary, in my specimens they are 

 always and only associated with the mesoglcea of the mesen- 

 teries. Fowler at the close of his account of Pocillopora 

 describes similar structures, and considers that they are rather 

 connected with the attachment of the mesentery to the corallum 

 than with the secretion of coral. My observations fully con- 

 firm his views. It is important to bear in mind that these 



