231 
PLUMULARIANS. 
cast out to enormous distances, intertwining and waving about 
in the water. At times a tuft may be seen slowly contract- 
ing, and I have observed one dragging down with it a mass of 
stuff which it had collected.* A specimen which I possess of 
an Australian Plumularian preserved in fluid, exhibits a really 
wonderful display of these thread-like organs, sheaves of 
which surmount a large proportion of the multitudinous “ cali- 
cetti,” and quite change the aspect of the hydroid (PI. CX., 
fig. 5). The Italian naturalist Meneghini, who first figured 
these organs (so far as I know), represents them in this condi- 
tion. From the aperture of every cup rises (in his figure) a 
tuft of very numerous tentaculoid appendages. The whole 
structure is not unlike a very delicate polypite, and as such 
he seems to have regarded it. 
No description can give an adequate idea of this wonderful 
apparatus as it appears when in full action. The Plumularian 
colony, indeed, offers us a remarkable combination of vital 
movements in the play of the polypites as they seek their food, 
the stealthy outgoings of the amoeboid processes as they slowly 
traverse the stems, and the rapid emission and extension of the 
waving threads. 
I may mention in passing that the thread-cell, which is 
eminently characteristic of Coelenterate organisms, has also been 
detected in some of the Protozoa. 
When we come to inquire into the function of the curious 
structures which I have just described, we are very much at 
fault. As the thread-cells are stinging organs, the superior 
lobes of the sarcode mass (or sarcostyle) may naturally be re- 
garded as so many forts with heavy armature placed for the 
defence of the colony. They may help to keep off carnivorous 
enemies, such as the naked molluscs ( Nudibranchs ), which are 
fond of browsing on the polypites of the Hydroida. But what of 
the amoeboid processes emitted from the lower lobe ? It seems 
not improbable that they may be subservient in some way to 
the work of nutrition ; or if not, they may be instrumental in 
keeping the surface of the plume free from impurities and 
foreign growths which might be detrimental to the well-being 
of the colony. Considering the immense number of the sarco- 
thecse and the various structures and activities connected with 
them, it is impossible to doubt that they must bear some 
important relation to the life of the hydroid. 
We may regard the amoeboid processes, I think — and this is 
their most interesting aspect — as a clue to the genealogy of the 
Hydroida, as evidence of a time when there was a much closer 
* Vide a paper by the author, entitled Contributions to the History of 
the Hydroida , u Annals of Nat. Hist.” for Nov. 1872. 
