Prof. Allman on Amcebiform Protoplasm in the Hydroida'. 203 



Pit by Iken Church. 



Ditto half a mile south-west of Calton farm. 



Brick-kiln one mile north-north-west of Aldbro*. 



N.B. Coralline Crag has also been found in digging atTrimley (authority 

 of the late Mr. Acton). 



XXI.-— Ow the Occurrence of Amcebiform Protoplasm, and the 

 Emission of Pseudopodia, among the Hydroida. By Professor 

 Allman, F.R.S. 



[Plate XIV.] 



One of the most striking peculiarities of the hydroids which 

 compose the family of the Plumulariada is the occurrence among 

 all of them of certain singular bodies which are produced as 

 buds at definite spots upon the hydrosoma. These bodies have- 

 been examined by Huxley* and also by Busk, who, from the 

 fact of their often containing clusters of large thread-cells, has- 

 named them "nematophores'^t- 



The most important character, however, of the nematophores 

 has hitherto escaped notice ; and yet it is one full of interest, 

 involving as it does the manifestation of phenomena whose 

 existence among the Hydroida has not as yet been suspected. 



The species which I have had an opportunity of most tho- 

 roughly examining are Aglaopheenia pluma [Plumularia cristata 

 of most authors) and Antennularia antennina ; and I shall con- 

 fine the present paper to a description of the nematophores and 

 their contents in these two hydroids. 



1. Aglaophcenia pluma. 

 In Aglaophania pluma there are two sets of nematophores — a 

 mesial and a lateral (PI. XIV. figs. 1-4). The mesial nemato- 

 phores {a a) are situated exactly in the mesial line, one being 

 placed in front of every hydrotheca. These mesial nematophores 

 consist each of a chitinous tube with peculiar contents. The 

 tube springs from the base of the hydrotheca, and, thence con- 

 tinuing for the greater part of its length adnate to the front of 

 the hydrotheca, terminates in a free tubular spine-like process a 

 little below the orifice of the latter. It opens below into the 

 common tube of the chitinous periderm; and just before its ter- 

 mination its cavity communicates by a lateral orifice with that 

 of the hydrotheca, while its free end opens externally by a very 

 oblique aperture. 



* Huxley, " On the Anatomy and Affinities of the Medusse," Phil. Trans. 

 1849, p. 427. 



t Busk, Hunterian Lectures (MS.), delivered at the Royal College of 

 Surgeons, London, 1867. 



14* 



