J J. LUCIUlNARIyE AND THEIR ALLIES. 



cess. The means, as it were, become the end. In the globose tip of the tentacles 

 cucli individual cell {fin. 88) constitntes the enormous depth of the layer at that 

 point where it lies, and tiie expansion of the peripheral end of the same cell is the 

 measure of the supei-ficial extent of the spheroid at that point. We have already 

 adverted (<[f 192) to an almost universal law among the AcidepTm, viz., that 

 each cellular wall is composed of a single stratum of cells, but did not point out 

 the inevitable result of such an arrangement, which is, as explained above, that 

 organs are formed, not so much by peculiar modes of aggregating multiplied cells, 

 as by varied modifications of comparatively few cells. This law becomes most 

 prominent to the observer when studying the inherent characters of the cells them- 

 selves; and we then lind that their essential qualities, such as they all have in 

 common, are more or less inseparable from their modifications. One instance will 

 suffice to illustrate this. The nucleus of the cells of the opsojjhragma occupies a 

 corresponding position in all of them, so that in a profile view {Jiffs. 88, 90, 91, 93) 

 of the thickness of this wall the nuclei appear arranged in a single line, about half- 

 way between the two ends of the cells ; but where these latter are so modified, in 

 the globose tip of the tentacles, that their depth is several times greater than their 

 breadth, the row of nuclei {fig. 88, cV) lies conspicuously near the peripheric end 

 of the cells. Here the proportions of the form are not alone modified, but also the 

 relative position of the contents of the cells. 



202 (A). When we consider the extreme mobility of the tentacles, as exhibited 

 in their powers of great elongation and high contractility, we cannot avoid infer- 

 ring that their component cells are adjustable in a commensurate degree between 

 the limits of these changes. This observation proves to be true ; but we could 

 hardly foresee that, besides varying in form, they would, at times, arrange them- 

 selves, or rather perhaps allow themselves to be arranged, in definite lines, or rows, 

 corresponding to the trend of the muscular fibrilltT? which underlie them. In a 

 word, we find that when a tentacle is contracted, the cells of tlie ectojyhrar/nnt not 

 only are broader in the direction of the contraction, so that their major diameters 

 trend parallelwise with each other, and consequently with the axis of the tentacle, 

 but tliey are also arranged in lines ( fig. 92, d) more or less regular, parallel with 

 the muscular fibrillae (wi^) (^ 98), and usually alternate with them, the latter being 

 slightly imbedded between the ends of the former. Now it would seem as if the 

 contraction of the whole mass would tend to compress the ectophragmal cells, so 

 that their major diameters would trend transverse to the axis of the tentacle, but 

 as it is not so we must infer that tlie lateral pressure is greater than the longitu- 

 dinal, yet we have to account for the linear arrangement of these cells, and their 

 evident connection, in this respect, with the muscular fibrillee. It would seem 

 plain enough that when these fibrillae contract they must of necessity decrease the 

 diameter of the adjoining cells, in the same direction as the contraction, and 

 throwing them sideways against each other, mingle them promiscuously ; but we 

 should not overlook the fiict that as a muscle contracts it broadens, and hence it 

 will exert a lateral pressure, and in doing so it will force the neighboring cells to 

 arrange themselves in lines on each side of it. 



We must also take into account the fact that the force of contraction operates 



