506 Scientific Proceedings, Royal Dublin Society. 



difficult to say without the examination of macerated preparations. 

 I have noticed a longitudinal striation of the mesogloea close to 

 the free end of the daotylozooid, but I cannot prove that this is 

 due to muscle- cells. Moseley says that the dactylozooids are 

 provided with " very long " muscular slips. In my preparations 

 I cannot trace these slips very far down into the pore. There can 

 be no doubt tliat these muscular slips correspond to similar struc- 

 tures occurring in the dactylozooids of Stylasfer, supported by the 

 serrated style. Like Moseley, I can find no trace of styles in the 

 dactylopores of Distichopora. 



At the free extremities of the tentacles of Distichopora there is 

 a thickening of the ectoderm, and a number of very small nemato- 

 cysts may be seen embedded in it. In all the Stylasteridee I have 

 examined I have been struck with the very small size of the nema- 

 tocysts, and in nearly all cases by their rare occurrence in other 

 parts of the colony than on the tips of the dactylozooids. 



The structure of the coenosarcal canal system of Distichopora 

 will be readily understood by reference to figs. 12 and 22 on 

 Plate XXX. of my last paper.^ On making a transverse section 

 through a decalcified secondary branch (fig. 12) one notices that 

 the canal extends from the periphery to a distance equal to about 

 one-third of the diameter of the branch towards its centre, leaving 

 a central space filled with the broken-down remnants of former 

 canals. In other words, in Distichopora as in Millepora (Moseley, 

 I.e. p. 24), only the superficial parts of the branch contain living 

 tissue, the centre or-axis being composed of dead coral. The 

 older the branch the smaller the proportion of living tissue. 

 Thus in the young pale tips living canals will extend almost 

 to the axis, whilst in the basal pieces of a colony there will 

 be only a narrow strip of coenosarc covering a thick axis of 

 dead coral. On making an examination with a one-sixth inch 

 objective of a section (fig. 22), the ectoderm may be seen to be 

 a thin nucleated sheath with fairly well-marked cell outlines 

 covering the surface of the colony and continuous with the ecto- 

 derm of the zooids. Between this and the endodermal canals 

 there is a dense tissue containing a few small nuclei — the me- 

 sogloea, and lying in the mesogloea are numerous and irregular 



1 1 Q. J. M. S., Vol. xxxir. 



