HYDROIDS. 



By L. a. Borradaile, M.A., Lecturer in Natural Sciences 

 at Selwyn College, Cambridge. 



(With Plate LXIX.) 



Three-and-twenty species of Hydroid Zoophytes were brought back from the Maldive 

 Islands by Mr Stanley Gardiner's expedition. Such a collection must at least have been 

 worth considering from the faunistic standpoint, but, as it happens, this is not the only way 

 in which the specimens have repaid examination. Some words at the outset on the points 

 of interest in the collection will therefore not be amiss. 



1. Two new facts are of some morphological importance as bearing on the relation of 

 the gonotheca to the hydrotheca, and therefore on that of the blastostyle to the ordinary polyp. 



There is in the collection a specimen of Lict.orella halecoides carrying its gonothecae, 

 which have hitherto been unknown. These gonothecae are remarkable by being in every 

 way like the hydrothecae save that they do not take part in the regular arrangement of 

 the latter and are nearly four times their size. Furthermore, though they do not, in the 

 specimen, contain gonophores, there is at the bottom of each of them a hydranth, perfectly 

 formed and to all seeming exactly like those in the hydrothecae except for its greater size*. 

 Indeed the suggestion arises that they may be giant hydrothecae and no more. But the 

 impression that they make is undoubtedly that of gonothecae, there seems no other reason 

 why giant hydrothecae should be found, and a strong argument for their having a gonidial 

 function is found in the fact that the blastostyles of another Campanularian, Halecium 

 halecinum, also carry hydranths at the end (2, p. 58). In that case, it is true, there are two 

 hydranths to the blastostyle, but meristic repetition will probably account for this. The ripe 

 gonotheca of L. scandens, though it is less hydrotheca-like than the present structure, is 

 enough so to bridge over the gap towards more specialised gonothecae, and it is particularly 

 interesting to notice that, according to Bale, its blastostyle has an open mouth (8, p. 759). 



The meaning of these facts is clear. There can now be no doubt, as indeed there was 

 little before, that the blastostyle is a modified hydranth, and the gonotheca a modified 

 hydrotheca. 



But while one species in the collection gives clear information on this point, there is 

 another which would seem to raise the whole question anew. A Synthecium (S. maldivense) 

 found in several of the atolls has gonothecae of the kind which characterise the genus. That 



1 The ordinary hydranths are not well preserved. 



