THE PTEROBRANCHIA OF THE SIBOGA-EXPEDITION 



WITH AN ACCOUNT OF OTHER SPFXIES 



BY 



SIDNEY F. HARMER, Sc. D., F. R. S. 



Fellow of King's College, Cambiidge, and Supeiintendeut of the University Museum of Zoology. 



With 14 plates and 2 text-figures. 



I. INTRODUCTION and HISTORICAL. 



Among the organisms obtained during the voyage of H. M.S. "Challenger" in 1873 — 1876, 

 one of the most striking novelties was the animal described by M'Intosh (82) as Cephalodiscns 

 dodecalopJius. It was trawled at Station 311, in the Straits of Magellan, at a dejath of 245 

 fathoms, from a bottom consisting of blue mud. The gelatinous tube, or coenoecium, contained 

 large numbers of female individuals, and many free eggs; but no tracé of a male was to be 

 found. The affinities of the organism were entirely problematical. It was at first thought that it 

 might be a Compound Ascidian, while it was sent to Professor W. C. M'Intosh for examination 

 on the supposition that it was perhaps related to the Annelids. M'Intosh, with Allman and 

 BusK, arrived at the conclusion that its nearest affinities were with Rhabdopletira^ a result which 

 has been amply confirmed by the subsequent work which has done on the two genera. 



Cephalodiscns was introduced to science at the meeting of the British Association in 1882, 

 although the Report of that meeting containing the original description (M'Intosh, 83) did not 

 appear until the following year, and was thus preceded by the fuller "Preliminary Note", published 

 by Professor M'Intosh in the "Annals and Magazine of Xatural History" (82). There was at 

 this time a general consensus of opinion that Rhaèdopleura belonged to the Polyzoa, although 

 constituting an aberrant type; and there was at first no reason for suspecting that this genus 

 and Cephalodiscns had affinities in a widely different direction. The preliminary notes gave an 

 account of the coenoecium and of its contents, the "polypides", the free ova and the buds. 



SIBOGA-EXPEDITIE XXVI i^iV. I 



