LUCE RN A RLE AND THEIR ALLIES. 109 



the doors of the nematocysts, to give warning of the approach of any foreign 

 body. 



20-t. 3Imcular Flhrilke (^98) {fujs. 91, 92, lm\ 2;M^ ;3«t=).— Notwitlistanding 

 that these librilkc exhibit a quite marked tendency to arrange themselves in fasci- 

 cles, as if to form a distinct organ, like tlmt in the peduncle (^[ 59, 88, 199), 

 we meet with no trace of intermixture of such cells as are so abundant in the 

 latter. The fibrillse of the tentacles are remarkably distinct from all surrounding 

 tissue, both as a wliole and as regards their component elements, the elongated, 

 fusiform cells. Their only connection with the ectopbragma (;«'), on the one hand, 

 and the chondromyoplax (//) on the other, is that of mechanical contact. 

 They are buried mostly in the peripheral surface of the chondromyoplax (/y. 91, 

 J'), and very slightly impress themselves on the inner face of the ectopbragma. 

 The cellular elements of a fibril are not so clearly apparent from that point of view 

 which regards them face-wise, i. e., looking in a line perpendicular to the layers 

 of the tentacles, as they then seem organically united with each other, end to end, 

 and do not allow their lines of junction to be seen. Taken togctlier, then, they 

 form an undulating thread, whicli is slightly swollen from point to point, with a 

 faint elongated nucleus occupying a large part of the lengtli of each swelling. 

 That these swellings correspond to individual cells, each containing a single 

 nucleus, may be proved by obtaining a view at right angles to this, that is, 

 observing them in profile (at 1 iiv) ; when they will have all tlie appearance of a 

 linear series of separate, fusiform bodies, overlapping each other at their pointed 

 ends. From this point of view, and in a transverse section {fig. 91, nr) also, we 

 can determine most satisfactorily that the fibril cells have no organic connection 

 with the chondromyoplax Q?). The amorphous, rigid fibrillte of the latter abut at 

 their broader ends witli a most decided line of separation between them and the 

 fusiform cells of the muscles. The two have nothing in common, unless it be the 

 intervening blastema ^^ylich constitutes the mould in which all cells are cast. (See 

 If 196.) 



205. The ClinndromyopJnx {% 196) {fifjs. 90, 91, V). — In immediate connection 

 with what has just been said, incidentally, in regard to this layer, we have only 

 to add a few words, particularly in reference to the function it possesses in the 

 economy of the organ to wliich it belongs. When discussing its qualities as a 

 layer (^j 65, 196) in the front of the unibella, we argued that it had rather the func- 

 tion of elastic connective tissue, without saying precisely liow it operated. In that 

 position it would more likely be subjected to traction than to compression, or at 

 least to a much greater degree. There can be no hesitation in deciding that in 

 the tentacles it acts as a resilient body, in counteracting the retractile force of the 

 muscles, and repressing, to a certain degree, the expansive force of water injected 

 into the tentacle from the main cavity of the body. Its prime value, however, is 

 felt when, by its great resiliency, it extends the tentacles to tlieir extreme length. 

 There are no annular muscles in these organs, and their longitudinal fibres can 

 only retract them, or flex them from side to side. The histological elements of 

 this layer are the same as in the umbella, and, as they have been described 

 (If 196) pretty full.y in tliat connection, we will not repeat the description here. 



