SUPPLEMENTARY NOTE. 



229 



him, but with the strong evidence ou tlie other side I must suspend my belief in the correctness of 

 his interpretation of the appearances here presented by liis dissections. 



Accepting, indeed, the statement of Schulzc, that the " Sliitzlamelle" can be traced over the 

 spadix, it will still, I believe, be found that the generative elements originate at the cndodermal side 

 of this membrane. In some instances, as in Laoinedca ca/iaiJaia, a hydroid with a branching spadix, 

 an extremely delicate, structureless membrane may, with careful illumination, be traced over the free 

 surface of the ova while these are still in contact with the spadix, and I now believe that it is the same 

 membrane wliich may, in some cases, be seen to be carried out, hernia-like, before the ova when these 

 are expelled under pressure from the gonojihore, and which I formerly regarded as probably representing 

 a condition of the vitellary membrane {see p. 64). Is not this the membrane which Schulze has traced 

 over the spadix, and which he regards as a continuation of the " Stiifzlamelle" ? If so, the ova must 

 have been produced between the " Stiitzlaraelle" and tlie spadix, and not upon the outer side of this 

 membrane, as maintained by Schulze. 



THE GONANGIUM. 



Among the hydroids in Mr. Busk's collection, which he placed in my hands for examination, is 

 a calyptoblastic species from New Zealand. Its trophosome, so far as its state of preservation in the 

 dried specimen allows of comparison, differs in no respect from that of a typical Sertularian, but its 

 gonosome presents the hitherto entirely unprecedented character of having its gonangia borne upon 

 peduncles, which spring from ivithin the hydrothec<g. 



The gonangia are oval, opening at their distal extremity 

 by a tubular orifice, and ornamented by curved ridges which 

 terminate at each side in a zigzag line, which runs down the 

 middle of the gonangium walls from the summit to the base. 

 Each gonangium is borne on a long cylindrical peduncle, 

 which springs from the bottom of a hydrotheca, in which it 

 occupies the position of a hydranth. TIjc peduncle extends 

 through the whole length of the hydrotheca, and as it nearly 

 equals it in diameter it almost fills its cavity. It is covered 

 by a delicate chitinous perisarc, and immediately, on emerging 

 from the cavity of the hydrotheca, carries the gonangium ou 

 its summit. 



Whether those hydrotheca; from which the peduncles of 

 the gonangia emerge ever carried hydranths, which subse- 

 quently became replaced by the gonosome, or whether they 

 have been all along exclusively devoted to the gonosome, it is 

 impossible to determine from dead and desiccated specimens. At all events, it is certain that there is 

 not a single point, either in position or in form, by which these gonangia-bearing hydrothecEe differ 

 from the others. 



The hydroid thus so very exceptionally constructed must constitute the type of a new genus and 

 species, to which the name of Synthecium elegans may be given. 



Sr/iifheciam elegans. 

 Ordinary hydrotheca destined for the reception 

 of a hydranth. a'. Hydrotheca in which the 

 liydrauth is replaced hy the peduncle of the 

 gonangium. 6. Gonangium. 



FUNCTION OF THREAD-CELLS. 



In the account given above (p. 108) of the alleged stinging property of the thread-cells, reference 

 ought to have been made to the researches of Mr. G. H. Lewes (' Sea-side Studies'), who has investi- 

 gated, both by observation and experiment, the thread-cells of various species of Actinia, with the 

 view of determining how far we are justified in attributing an urticating property to those bodies. 



Mr. Lewes decides against their alleged powers of urtication. He supports his view on the 

 admitted fact that thread-cells are often situated in places where it is impossible for them to exert such 

 powers, as well as on the further observation that in their number and development they present no 



