376 Prof. Allman on the Morj^liologrj 



in that part of the fossil which carries the appendages*, 

 a fact quite in accordance with what we know of the corbul^ 

 in the living hydroids ; for in these the hydrothec^e with their 

 accompanying nematophores are replaced by the leaflets of the 

 corbula, while the naked gonangia of other hydroids are never 

 accompanied by an atrophy or other alteration of the hydro- 

 tliecaj or neighbouring parts. 



In both the American and British specimens the appendages 

 in question seem to have been supported by a framework of 

 branched chitinous filaments which remain behind after the 

 destruction of the intervening membrane. The existence of 

 these filaments probably depends on the same morphological 

 conditions as those which determine the presence of the chiti- 

 nous axial rod; and it must be admitted that we have no 

 known analogy for them in any living hydroid, unless the in- 

 ternal narrow chitinous lamina which passes like a midrib 

 through the corbula-leaflet (fig. 5, F, e) admits of being com- 

 pared with them. 



This comparison of the appendages of Hall to the corbula- 

 leaflets of an Aglaoplienia is in hai'mony with the view here 

 advocated as to the nature of the calicles of the graptolite, 

 which we have compared to the nematophores of an Aglao- 

 jyhenia. I believe the corbula of the living Aglaojjhenue to 

 consist essentially of a special and excessive development of 

 the nematophores ; so that the graptolite, not only in its tro- 

 phosome, but also in its gonosome, would thus present us with 

 an instance of the great development of the nematophoral 

 system at the expense of the hydranthal. 



This view of the morphology of the corbula, in some cases 

 at least, seems placed beyond doubt by their formation in an 

 undescribed Aglaophenia from the deep-sea dredgings of the 

 United-States Coast Survey. The leaflets which form the walls 

 of the large and beautiful open corbulas of thishydroid are mainly 

 composed of the greatly enlarged and transformed nematophores 

 which in the unaltered ramulus lie in front of the hydrothecEe. 

 Thehydrothecse of the parts which become transformed into cor- 



* Hall notices a case {loc. cit. p. 33, pi. b. fig. 9) whicli lie regards as 

 one in which the appendages are present in a graptolite which still retains 

 its denticles. This, however, is by no means a well-marked instance, 

 and one might be permitted to doubt the identity of the structures here 

 figured with the appendages previously described by him. In Mr. Hop- 

 kinson's woodcut also, the denticles are represented as well developed for 

 some distance on that part of the graptolite which carries the appendages ; 

 I cannot satisfy myself as to the reality of this in the actual specimen ; 

 indeed the woodcut does not do justice to the excellent original drawing 

 kindly sent to me for inspection by Mr. Ilopkinson. 



