500 Scientific Proceedings, Royal Dublin Society. 



(PI. XX. fig. 2). I have been unable to determine whether these 

 muscles are ectodermic or endodermic in origin, but when we 

 compare them with similar structures in Distichopora there is 

 reason to believe that they are ectodermic. If this is the case 

 tlien the endoderm is entirely obliterated in '' the muscular slip," 

 part of the dactylozooid of Stylaster. 



The only specimen of Stylaster I have had an opportunity of 

 examining belonged to a female stock. The ripe eggs are 0"25 

 mm. in diameter, being considerably smaller than the the eggs 

 of DisticJiopora (0-3 to 0*4 mm.), and Allopora (0-5 mm.)^ 



The ovum contains, as in other Hydrocorallines, a large 

 quantity of yolk, and in the process of maturation, fertilization, 

 and the early part of the development, it exhibits similar pheno- 

 mena to those I have already described elsewhere in Allopora and 

 Distichopora. The trophodisc does not need any special descrip- 

 tion. It resembles in all the essential features of its formation 

 and structure that of Allopora (PI. xx. fig. 3). 



I have no knowledge of the structure of the male gonophores 

 of this species, but it might be useful to repeat here Moseley's 

 brief reference to the male gonophores of S. densicaulis. He says : 

 " Only male specimens of S. densicaulis were obtained. Each male 

 ampulla contains two or three ovoid gonophores which are attached 

 to large offsets of the coenosarcal meshwork at one end of their 

 longer axis. They have an internal spadix, and in finer structure 

 seem to differ very little from those of SporadoporaP From the 

 last sentence it seems clear that the male gonophores of Stylaster 

 densicaulis are similar in general structure to those of Allopora. It 

 should be remembered that I have abandoned the use of the term 

 spadix and adopted the word trophodisc for Moseley's " ciip-shaped 

 spadix," and manubrium for the " internal cylindrical spadix." 



I have previously pointed out that in the male gonophores of 

 Distichopora there is no manubrium, and that in the male gono- 

 phores of Allopora there is a very prominent manubrium. Both 

 from the text and the figure given of Sporadopora it is clear that 

 Stylaster densicaulis possesses a well-marked manubrium in the male 

 gonophore. 



1 In all cases I have taken the longest diameter of tlie ovum, i.e. the diameter 

 parallel with the surface of the corallum. 



