244 CONTRIBUTIONS TO THE NATURAL HISTORY 



artificial pressure, long threads, bj which they no doubt seize upon their prej ; as it is never 

 observed that they coil the whole tentacle round any animals which they strike to death 

 apparently by simple contact, and which remain adherent to the part of the tentacle 

 with which they have been struck. This shows plainly that the nettling cells them- 

 selves, with their threads, must be the seizing apparatus ; and though I have never seen, 

 in the living animal, the threads turn out of the cell in this species, and have only 

 noticed it in specimens acted upon by pressure, I have recently observed the fact of the 

 inversion of the netding cells in Polypi so distinctly, that I have no doubt as to the 

 identity of the operation in both cases. 



The discovery of these netding lassos in so many animals provided with tentacles, 

 and which had never been seen to use their tentacles to secure their prey, but which 

 seemed rather to retain it by some magic power, will at once account for all the dif- 

 ficulties. Though the tentacles taper uniformly for their whole length, they are com- 

 paratively rather thickened near the base, where their swollen wall forms a kind of sup- 

 port for the numerous minute pigment-cells which constitute the bulb of the eye, among 

 which a few pigment-cells, of a larger size, grouped closely together, constitute a dark, 

 brilliant speck upon the outer and upper part of this bulb. This is another curious 

 adaptation in nature, where the organ of sight is combined with one which is destined 

 to catch the prey, and where the main apparatus for distinguishing at least between light 

 and darkness, if not for perceiving distinct images, is imbedded in a heap of cells, which 

 form also part of the thick wall of the tube through which the fluids circulate. This 

 combination is so remarkable, that it is worth while to pause a moment and consider the 

 particular disposition of this bulb, its intimate structure, and its relation with the dif- 

 ferent parts around it. 



The sensitive bulb, as I may call it (Plate V. Figs. 12, 13, and 14), is placed, as al- 

 ready mentioned, at the junction of the marginal tentacles and the circular vertical 

 tube, which pass into each other on their inner surface. It forms a marked projection, 

 and is of an irregular triangular form, with rounded edges. Seen from below (Figs. 2 and 

 4), it is divided into two halves bulging sideways, between which the marginal tentacles 

 arise (Fig. 13). Seen in profile (Fig. 13), the dark eye-speck appears still more promi- 

 nent, in the shape of a hemispherical body projecting above the base of the tentacle. 

 Seen from above and outside (Fig. 14), it is more pear-shaped, the vertical tube, a, above 

 the eye-speck appearing like a continuation of its upper end. The circular tube (Fig. 

 13, c) opens sidewise towards its lower margin, and so far behind its edge as to appear 

 less connected with it on each side when seen in front. (Fig. 12.), The whole mass of 

 the swollen bulb consists of various kinds of pigment-cells, and other cellular uncolored 



