42 



LUCEKNARI^ AND THEIR ALLIES. 



umbella, as if its constituent layers had been pushed outward, at stated points, into 

 finger-like projections, and had become fixed there. Such we may see they are, 

 essentially, if we follow their course of development— their budding— as anyone can 

 do, either with young specimens or old ones in hand. The groups into which they 

 are gathered number eight in all, and are situated singly on each corner {^*) of 

 the octagonal umbella, close to the marginal junction of its circumoral and aboral 

 parietes,' the bases of the older, most distal tentacles (////. 54, D) actually abutting 

 against the margin of the latter. They are, however, distinctly separate from 

 .that, not only by virtue of their position, but also in the quality of their walls; 

 and prove to be, in their minuter details, identical in kind with the layers of the 

 circumoral parietes from which they arise and are directly prolonged. From a 

 taxonomical point of view they are very peculiarly situated, no single bunch being 

 complete in regard to symmetry, neither in reference to the relative position of the 

 tentacles among themselves, nor in their relative ages and sizes. In as few words 

 as possible we express their arrangement by saying that they are one-sided, asym- 

 metrical bunches. Yet their very asymmetry is symmetrical ; for if, of two groups 

 adjoining a partition (i^-), one group preponderates on the side nearest that parti- 

 tion, the other also leans toward it, and thus they present a symmetrical relation to 

 each other similar to what we find in the anisoscelean triangular halves [X) of the 

 genitals. If we combine, now, the functional relations of the regions comprising the 

 genitalia with the apparent taxonomical mutual reference of the tentacular groups 

 which lie opposite those regions, it becomes evident that the umbella is subdivided 

 into four symmetrical portions, each separated from the other by the areas which 

 extend from the corners (t,'') of the proboscis to the margin. Such a prominent 

 relationship would seem to demand that these subdivisions should stand in the 

 principal planes dividing the body into right and left, and into dorsal and ventral 

 segments ; yet, not only would the animal be just as symmetrical if divided along 

 the planes intermediate to these, i. e., planes prolonged from the corners (^') of the 

 proboscis, but there is every reason to believe that the latter way would be the 

 right one. Why this is so cannot be entered into here, but our reasons for so 

 believing may be found, expressed in full, in the section (Part XV) on the " crite- 

 rion of symmetry." 



90. Taxoaomf/.—The asymmetry of the groups of tentacles referred to in the 

 last paragraph may be most conveniently illustrated in the mode and succession of 

 development of these organs in the young, before they become so numerous and 

 crowded as to render their relations to each other more multiplied and complicated. 

 A special section or paragraph (149, 150, 155) has been devoted to this in a 

 subsequent cliapter (VI), and for the sake of clearness we would ask the reader's 

 perusal of that part of the- subject before proceeding with what we have now to 

 present. The guide to the disposition of the members of each group is a single 

 tentacle, situated on tlie distal side, and, as near as the eye can judge, about 

 opposite the mi.ldle of the bunch (figs. 17, 22). We should state, before proceed- 

 ing farther, that the usual number of tentacles in the adults is about one hundred; 

 but not mfrequently very large specimens are met with which possess as niany as 

 one hundred and twenty in each bunch. Now, for certain purposes, such multitudes. 



