KEPORT ON CORALS — HYDROCORALLINvE. 31 



The hard tissues are transversed in all directions by fine capillary branching canals which 

 are provided at intervals with numerous spherical cavities attached to them laterally 

 (PI. XIV. figs; 6, 8). In Millepora alcicomis, from Bermuda, in which the ccenosteum is 

 comparatively soft and cancellar, borings of the parasites could only here and there be 

 detected. When set free by acids the organisms are seen to consist of ramifying 

 mycelial threads, with abundance of fructification. Their structure has been described 

 at length by Professor Duncan. It is remarkable that they have a distinctly green colour. 

 They are not confined to the calcareous structures, but in Millepora nodosa at least, 

 occur also in abundance amongst the soft superficial tissues ; and it appears probable that 

 they become included within the calcareous tissue by the calcareous matter being 

 deposited around them as the coenosteum is extended by growth. 



SECTION II.— ON THE STRUCTURE OF THE STYLASTERID^E. 



WITH A LIST OF ALL THE SPECIES OF THE FAMILY AT PEESENT KNOWN, AND 

 DESCEIPTIONS OF SOME NEW SPECIES OBTAINED BY H.M.S. CHALLENGE!:. 



Introduction. 



In the Proceedings of the Royal Society, No. 172, 1876, I published a preliminary 

 note on the present subject, and gave a short account of the results which I had arrived 

 at from a somewhat hurried examination of the material at disposal. After this short 

 account had been written, I devoted my time during the remainder of the homeward 

 voyage of H.M.S. Challenger to the further study of the structure of the Stylasteridse, and 

 the preparation of drawings illustrating it ; I have supplemented this by additional work 

 in England, and the results are embodied in the present paper. 1 The main part of 

 the specimens of Stylasteridse, from the study of which the anatomical details were 

 determined, was obtained at a single haul of the trawl-net taken on February 14th, 1876, 

 in lat. 37° 17' S., long. 53° 52' W., off the mouth of the Rio de la Plata, in a depth 

 of 600 fathoms. The specimens then obtained included six genera of the family 

 Stylasteridas. They were in most excellent preservation, although they had been slowly 

 raised from the bottom, and in all the genera but one the generative organs were in full 



1 The greater part of this present treatise is a reprint of tie Croonian Lecture for 1878, On the Structure of the 

 Stylasteridae (Phil. Trans. Roy. Soc., part 2, 1878, p. 42.3), which was published in advance in the Philosophical Transac- 

 tions by the permission of the Lords Commissioners of the Treasury. 



