( 257 



VI. — The Morphology and Development of the Free-swimming Sporosacs of the 

 Hydroid Genus Dicoryne (including Heterocordyle). By J. H. Ashworth, 

 D.Sc, University of Edinburgh, and James Ritchie, M.A., D.Sc., Royal 

 Scottish Museum, Edinburgh. 



(Read June 21, 1915. MS. received August 25, 1915. Issued separately December 10, 1915.) 



[Plates VI-VIII.*] 



CONTENTS. 



Introduction , . 



Dicoryne conybearei, General Description of 



Colonies ...... 



Stolon : Regenerative Capacity of the Stolon 



Hydrocaulus and Hydranth 



Blastostyles ...... 



Development of the Sporosacs . 



The Sporosacs of Dicoryne conferta . 



Affinities of the Free-swimming Sporosacs 



Dicoryne conybearei ..... 



of 



PAGE 



257 



258 

 259 

 260 

 261 

 263 

 266 



269 



A Discussion of the Homology of the Sporosacs of 

 Dicoryne ........ 



Abnormal Sporosacs of Dicoryne conybearei 



Early Developmental Stages of Dicoryne conybearei . 



Distinctive Characters of the Species of Dicoryne 



Specific Characters of Dicoryne conybearei 



emend 



Dicoryne, Allman, char, emend. 

 List of Works Quoted 

 Description of Figures 



(Allman), 



271 



277 

 278 

 280 



282 

 282 

 283 



284 



Introduction. 



Hitherto there has been described only a single species — Dicoryne conferta 

 (Alder) — amongst the Hydrozoa in which the reproductive body is a sporosac which 

 becomes^ ciliated and free-swimming. We have found that another species which, 

 as we shall show (pp. 269-271), must be named Dicoryne conybearei gives rise to 

 reproductive ' bodies of this type, which, however, differ from those of Dicoryne 

 conferta in several important respects. The free-swimming type of sporosac has 

 not been the subject of close observation since 1872 ; we have therefore made 

 as complete a study of the structure and development of the sporosacs, especially 

 of D. conybearei, as material gathered from several sources would permit. 



The material of D. conybearei at our disposal consists of colonies on seven 

 gastropod shells,! dredged off the island of Nisida, in the Bay of Naples, in April 



* The cost of the blocks for text-figs. 2 and 3 and of reproduction of the plates has been defrayed by a grant 

 from the Carnegie Trust for the Universities of Scotland, and we are further indebted to the Trust for a grant for 

 artistic assistance in connection with Plate VI. 



t The specimens were brought to the Naples Zoological Station, and handed, along with other hydroid material, 

 to Mr T. J. Anderson, who was at that time studying the Hydrozoa while holding a Carnegie Scholarship. 

 I was working in the Naples Station at the same time, and, on seeing these colonies and their sporosacs, realised, 

 as did Mr Anderson, that they presented several new and interesting features. Mr Anderson left Naples shortly 

 afterwards, and, before he had been able to work further at the material, went to Nairobi to take up the 

 appointment he now holds. On his departure he kindly placed the specimens in my hands. Unfortunately, 

 Mr Anderson did not make any notes on the colours of the colonies, or on the movements of the sporosacs, so 

 that on these points I have merely impressions derived from glimpses of the specimens in the brief intervals of my 

 own work on other subjects. — [J. H. A.] 



TRANS. ROY. SOC. EDIN., VOL. LI, PART I (NO. 6). 37 



