Prof. Allman on Amebiform 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 at Trimley (authority 
of the late Mr. Acton). 
XXI.—On the Occurrence of Amebiform Protoplasm, and the 
Emission of Pseudopodia, among the Hydroida. By Professor 
Auman, F.R.S. 
[Plate XIV. ] 
One of the most striking peculiarities of the hydroids which 
compose the family of the Plumulariade 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 contaiming clusters of large thread-cells, has 
named them ‘‘ nematophores” +. 
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 Aglaophenia 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. Aglaophenia pluma. 
In Aglaophenia pluma there are two sets of nematophores—a 
mesial and a lateral (Pl. 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 Medusz,”’ Phil. Trans. 
1849, p. 427. 
+ Busk, Hunterian Lectures (MS.), delivered at the Royal College of 
Surgeons, London, 1857, 
14% 
