and the Emission of Pseudopodia, among the Hydroida, 205 



3. Antennularia antennina. 



In Antennularia, a genus possessing the closest affinities with 

 Plumularia, phenomena entirely similar to those just described 

 in Afflaophania may be witnessed. 



In Antennularia antennina (PI. XIV. fig. 5), a pair of conical 

 cup-shaped nematophores {b) spring from the hydrosoma on a 

 level with the mouth of every hydrotheca ; while between every 

 two hydrothecse there also occur three similar, but azygous, 

 nematophores {a), which are arranged mesially along the front 

 of the ramulus. The nematophores of Antennularia differ from 

 those of Afflaophania in the fact of their being each attached to 

 the hydrosoma only by their narrow extremity, while from this 

 point they are free for their entire length. They terminate at 

 their distal or wide extremity in a hemispherical cup-like de- 

 pression, whose bottom is formed by a chitinous membrane 

 constituting a diaphragm which separates the cavity of the cup 

 from that of the rest of the nematophore. This diaphragm, 

 however, is perforated by a circular aperture in its centre. The 

 nematophore is thus bi-thalamic, consisting of two chambers — 

 a proximal deeper and narrower one, and a distal wider and 

 shallower one, the two freely communicating through the per- 

 foration in the dividing diaphragm. 



The whole nematophore is filled with a granular protoplasm, 

 which is continued from one chamber into the other through 

 the perforated diaphragm. In the distal chamber, it forms, 

 when in a state of repose, a little spherical mass {d) ; but there 

 does not occur in the nematophores of Anterinularia any special 

 accumulation of large thread-cells, as in those of Aglaophcenia 

 pluma, and only a few minute thread-cells may be seen scattered 

 through the protoplasm. 



When a living branch of Antennularia antennina is examined 

 in a trough of sea-water under the microscope, the mass of 

 protoplasm which occupies the distal chamber may be seen, in 

 both sets of nematophores, to slowly elongate itself into a 

 variously shaped process {dJ, e), exactly like the pseudopodium 

 of an Amoeba. When this process meets the external surface of 

 the ramulus, it frequently runs in contact with it for some dis- 

 tance, and, while we continue to look, the whole will be again 

 slowly withdrawn, until it once more assumes the form of a 

 spherical mass filling the cup-like distal chamber of the nemato- 

 phore. The pseudopodial processes of the nematophores in 

 Antennularia antennina are usually simple ; in one instance only 

 did I witness what seemed to be a short irregular branch given 

 off from the finger-like pseudopodium. 



EXPLANATION OF PLATE XIV. 

 Figs. 1-4. Hydrotheca with polypitc and neighbouring parts in AglaophcBnia 



