26 Prof. H. J. Clark on Lucernaria. 



which is embraced by the outer and inner walls of this floor, or, 

 rather, between the muscular layer and the inner wall : instead 

 of repeating, as occurs in Aurelia, the peculiarities of the gela- 

 tiniform layer of the aboral floor, it has a totally difi"erent ap- 

 pearance and consistency, and an almost unlimited degree of 

 expansion and contraction. In the tentacles it occupies a very 

 deep space between the outer wall, or, rather, the muscular layei-, 

 and the inner wall. In this latter respect, Lucernaria is again 

 peculiar, since, in addition to the muscular layer, which alone is 

 present in the young, it developes this gelatiniform layer — the 

 musculo -gelatinij or m layer, as I propose to call it — the like of 

 which does not exist in the tentacles either of Steganophthalmata 

 or Gymnophthalmata. In the aui'icles we have also a special- 

 ization peculiar to Lucernaria ; for, in addition to the pigment 

 eye-spot which is imbedded in the base of the oral face of these 

 bodies, the auricles, which in the young cannot be distinguished 

 from the tentacles, gradually thicken the outer wall as age ad- 

 vances, and peculiar granuliferous adhesive vesicles are deve- 

 loped between the cells. In the adult their tentacular nature 

 is almost or altogether obliterated, and the swollen outer wall, 

 together with the enormous thickness of the musculo-gelatini- 

 form layer, forms an oval mass, thickly studded with adhesive 

 organs, by which they cling in a most tenacious manner to any 

 body which they may touch. These organs and the base of the 

 peduncle are the only means of adherence which Lucernaria 

 possesses; although it is true that the tentacles are used, as 

 in Aurelia, for prehension, they are comparatively very weak, 

 and can only serve to retain the prey, and never effect the pur- 

 pose for which the auricles are constructed*. In consideration 



* The nettling organs, or lasso-cells, which crowd the globular tips of 

 the tentacles, are of two kinds, and both are imbedded in the intercelkdar 

 substance which fills the spaces between the columnar cells of the outer 

 wall. One kind consists of an oval thick-walled vesicle, about o oVo^ of an 

 inch long, or a little less, one end of which is introverted, and projects, in 

 the form of a stout hollow shaft, along the axis of the cell about four-fifths 

 of its length, and then, rather suddenly thinning into a slender thread which 

 also is hollow, it bends upon itself, returns nearly to the aperture of the cell, 

 and, pressing closely against the inner face of the cell-wall, it forms a close 

 coil which terminates at the end opposite the mouth of the introversion. 

 When the coil of thread is ejected, which is accomplished by sliding through 

 the hollow axial shaft, which in its turn retroverts also, just as the finger 

 of a glove is turned inside out, the whole aspect of the apparatus is changed. 

 The oval cell is considerably diminished in size, and from its aperture the 

 enormously enlarged hollow shaft projects in a straight line; the half of 

 the shaft next the cell is cylindrical, and half as broad as the latter, with 

 a slight expansion where it joins the mouth of the cell; the distal half 

 abruptly expands into an oval form, half as broad again as the cylindrical 

 portion, and rapidly tapers into a smooth, trihedral, twisted thread. The 



