Rev. T. Hincks on the History of the Hydroida. 387 



the same time the portion containing the thread-cells stands 

 out as a well-rounded prominence above the margin of the cup, 

 while the extensile lobe originates at one side of it, a little 

 below the summit. I have observed the same structure in 

 Plumularia pinnata. 



The division of the sarcode-mass towards its upper extremity 

 into two processes with different functions is very apparent in 

 the mesial nematophore, which adheres to the front of the 

 calycle in Aglaophenia jpluma. In this case the chitinous tube 

 of the nematophore is not merely furnished with a terminal 

 aperture, but also communicates with the cavity of the calycle 

 to which it is attached. The lobe bearing the thread-cells ex- 

 tends to the top of the tube; the extensile (or inferior) lobe 

 only to the point where this communication exists, and here 

 it discharges itself into the calycle, as noticed by Allman, who 

 does not seem, however, to have recognized the constant diversity 

 of function in the two branches of the granular mass. 



Kirchenpauer has described certain species of Aglaoj^hema 

 in which the tube of the anterior nematophore has a second 

 orifice, placed generally near the point at which it begins to 

 stand off from the calycle ; this orifice does not communicate 

 with the cavity of the hydrotheca, but affords a passage for the 

 extensile lobe into the surrounding water. He proposes to de- 

 signate nematophores of this kind " double-mouthed " (zxoei- 

 miindige). This observer does not seem to have noticed the 

 bilobate structure of the lateral nematophores, which I have 

 just described. 



We may distinguish, then, in the nematophore: — (1) the chi- 

 tinous case, which maybe simple (PI. XX. fig. 1) or compound 

 (fig. 2), and, if simple, furnished with one orifice only or with 

 two ; and (2) the soft granular oftshoot from the ectoderm per- 

 vading it, which may be either entire and destitute of terminal 

 thread-cells, or divided into two lobes above, one bearing 

 thread-cells and the other extensile. 



The protoplasmic processes which are emitted by the inferior 

 lobe have been well described by Allman. They are very 

 mutable, and exhibit frequent changes of form, often attaining 

 a great length. Sometimes they are cylindrical and slender, 

 stretching along the stems and branches, to which they are 

 closely appressed and along which they glide slowly, almost 

 imperceptibly, in AmoebaA.i^Q. fashion ; sometimes they appear 

 clavate at the extremity ; sometimes they swell out at intervals 

 into bulbous dilatations. Occasionally they may be seen to 

 reach across to a neighbouring branch and fix the extremity 

 upon that ; and rarely they give off two branches at tlie top, 

 which move in opposite directions (PI. XX. fig. 3, 5). I have 



