XIV. The Croonian lecture. —On the structure of the stylasteridæ, a family of the hydroid stony corals

Abstract

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 Stylasteridæ, and the preparation of drawings illustrating it. I have supplemented this work by additional work in England, and the results are embodied in the present paper. The main part of the specimens of Stylasteridæ, 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 Bio de la Plata in a depth of 600 fathoms. The specimens then obtained included six genera of the family of the Stylasteridæ. 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 development. It was the examination of this set of specimens which first convinced me that the Stylasteridæ were Hydroids and not Anthozoans, a fact which I had already been led to suspect from the structure observed in the case of a species of Astylus obtained from 500 fathoms off the Meangis Islands, and that of a Cryptohelia , a short reference to which was given in a paper “On the Structure and Relations of certain Corals” (Proc. Roy. Son, No. 64, 1875, p. 64, and Phil. Trans., Vol. 166, Pt. I., 1876, p. 116). I have examined also other specimens of Stylasteridse obtained by the dredge and trawl of the ‘Challenger’ in various parts of the world, and a few specimens from those obtained by the United States dredging expeditions, which have been generously placed at my disposal by Mr. Alexander Agassiz and Count de Pourtales of the Museum of Comparative Zoology of Cambridge, Massachusetts. Literature of the Subject. The family Stylasteridæ was formed by the late Dr. Gray in his "Outline of an Arrangement of Stony Corals” (Ann. and Mag. Nat. Hist., vol. xix., 1847, p. 127). The family was made to contain the genus Stylaster alone, and was thus characterized:— “Coral minutely porous, cells deep, cylindrical, with six grooves, each ending in a pore and a central style.”