388 E.ev. T. Hincks on the History of the Hydroida. 



observed them in a state of great activity, as I have mentioned 

 elsewhere, on a young specimen of Plumulariafrutescens^ which 

 they completely invested with " a multitude of gossamer-like 

 threads." These extraordinary prolongations of the granular 

 mass in the nematophore can be entirely withdrawn. 



The action of the thread-cells on the superior lobe is much 

 more rarely witnessed ; Meneghini seems to have noticed it, 

 but without comprehending its true nature. On a specimen 

 of Aglaophenia fluma I have seen the contents of the nemato- 

 cysts discharged, and the long delicate threads streaming up- 

 wards from the extremity of the lateral neniatophores (PI. XX. 

 fig. l,a). These line extensile lines were cast out to enormous 

 distances, intertwining and waving about in the water ; three 

 or four were usually emitted from each cluster of thread-cells ; 

 and in some cases I noticed that the cyst itself was raised to 

 some height above the nematophore and borne on a slender 

 pedicle. At times a tuft of the threads might be seen slowly 

 contracting, and I have observed one dragging down with it 

 a mass of stuff which it had collected. 



The sight of this wonderful apparatus in full action was 

 singularly interesting, and it was impossible not to feel that it 

 must bear some important relation to the life of the Hydroid. 

 I may mention that the specimen on which the thread-cells 

 were in action showed no trace of pseudopodia. 



It is difficult to form a conjecture as to the function of these 

 curious appendages. They have been regarded as organs of 

 defence ; and Kirchenpauer proposes to rank them with the 

 polypites and gonozooids of the Hydroid colony under the name 

 of the " defensive zooids" [WehrtMere). But it seems to me 

 very doubtful whether this is the true interpretation of the ne- 

 matophore. I am inclined to think that its function may be 

 in great measure nutritive ; the pseudopodia at least seem much 

 better fitted for the work of alimentation than for that of 

 defence. 



If we may accept Prof. Allman's very ingenious theory of 

 the structure of the fossil Graptolites, we shall have important 

 evidence in favour of this view. He regards them as morpho- 

 logically Plumulariidans in which the development of hydro- 

 tliecaj has been suppressed by the great development of the 

 nematophores *. In short, according to his interpretation, they 

 were Plumulariidans in Avhich the ordinary alimentary zooid 

 (the polypite) was wanting, and the function of nutrition pro- 

 bably devolved altogether on the nematophores. If this view 

 be correct we shall have, as Allman has remarked, in the 



* 'Monograph of the Gvmuoblaslic or Tubularian Hydroids.' part ii. 

 n. 170. 



