HYDROIDA II 



43 



Examination of a large amount of material leaves no doubt as to the correctness of this. The species 

 is enormously multifarious in its power of variation, and has a remarkable capability of changing its 

 appearance; an examination of the branches, however, will always reveal the characteristic, almost 

 spherical apophyse typical of the species, and the distinguishing characters established are seen to be 

 founded on growth stages. 



Dons does not appear to have noticed that his figure D. 5 shows how the male gonotheca 

 can be formed in hydrotheca as a heteromorphotic renovate. This is particularly interesting in the 

 case of the present species, since other heteromorphotic renovates likewise appear in the same in nature, 

 as tendril-like stolon formations in place of hydranths. Dons mentions such renovates, with illustra- 



2oo m. ftoom. .-. _._ looom. looom. 



Fig. XVI. Localities of HaUcium curvicaule in the Northern Atlantic. 



tions, and points out that these very features have served as the basis on which the species Halecium 

 mirabile was established. The species is thus characterised by a less lively hydranth renewal, but has 

 on the other hand a more marked tendency to form heteromorphotic renovates than most other forms 

 of Halecium. 



Halecium curvicaule is a markedly high-arctic species, belonging to the littoral region. Only 

 quite exceptionally does it penetrate into boreal waters (fig. XVI) as for instance at Iceland. Off the 

 coast of Norway it has not yet been met with south of Bjark0y. 



Halecium muricatum (Ellis and Solander) Johnston. 

 1786 Sertularia muricata, Ellis and Solander, The natural history of many curious an uncommon Zoo- 



phytes, p. 59, pi. 7> % s - 3~ 4- 

 1847 Halecium muricatum, Johnston, A history of the British Zoophytes, p. 60, pi. 9, figs. 34 



