34 



LUCKKNARI^ AND THEIR ALLIES. 



across tlic angles of the umbella disclose a rigid uniformity in the thickness of 

 tlic cliondvophys, and at the same time expose the abrupt, marginal juncture of the 

 latt(>r with the'chondromyoplax, as explained in a former paragraph (66). 



78. Tlie double layer (70) which we have comprised under the name chondrophys, 

 possesses certain dissimilar characteristics in each of its subdivisions, Avhich lead us 

 to describe them as if separate, although we do not believe that they are originally 

 of diverse origin. We shall defer giving the details regarding these (^f 197) until 

 we come to the histological anatomy of this animal, and content ourselves with 

 merely indicating the appearances which first catch the eye upon a cursory survey 

 of the mass. In any of the sections mentioned above, it will be noticed that the 

 chondrophys is composed of a comparatively thin layer (c'), which forms the inner 

 division, and of a very thick stratum (c), which is at least four to six times as thick 

 as the other. It is a peculiarity of the thinner one that it terminates with a sharp 

 edge {fi(js. 60, 61, 62, c^) at this point of junction of the anterior and posterior 

 l)iu-ietes of the umbella, and therefore bears no part in forming the abrupt margin 

 of the chondrophys. Again, the striations which traverse the thickness of this 

 layer are much finer and closer together than those in the thicker stratum, and 

 moreover they always, even in the peduncle, trend in one direcion, i. e., in parallel 

 lines from face to face; whereas those of the greater mass are comparatively heavy, 

 and are remarkable for the regular and systematic manner in which they cross 

 each other about the axis of the peduncle {fi<j. 52, c'), there being no less than 

 five distinct sets of decussating fibres at this point. (See *\ 198 for details.) 



74. The gastromyopJax (PI. vii,». 74, 77, o; PI. iyi,figs. 98, 99, 103, A).— For 

 the purposes of homology this term is better suited than another {oumijopJax, ova- 

 rian muscular layer) which would signify the restricted limits of this layer in the 

 region of the reproductive organs of Lucernaricv. It is essentially an oomyoplax 

 because it is developed only in and about the genitalia, and cannot be traced be^ 

 yond the outskirts of the saccules (^j 51) and the digitiform bodies (^f 52). In regard 

 to the latter, the presence of this layer in them as well as in the saccules tends to 

 confirm their association as a part of tlie reproductive organs. But the o6myoi)lax 

 is homologically identical with the gastrorayoplax of the Strobiloid medusa-cephaloid, 

 whose true oomyoplax is incorporated with another layer — the opsomyoplax. The 

 term oomyoplax, then, can be used only as indicative of function and not of 

 structural relation. We shall scarcely do more here than mention this layer, 

 because it forms a part, though small, of the body-wall, and refer for all the neces- 

 sary details to the paragraphs (135-137) on the reproductive organs, to which it 

 strictly belongs in Lucernarife. As the muscular cords emerge from the chondro- 

 phys of the peduncle and cut their way through the chondromyoplax (see ^ 59 and 

 67) to enter the proximal ends of tlie partitions, a thin film of muscle is given off, 

 just behind the base of the proboscis {fig. 47% p-^), and extends into the nearest 

 digitiform bodies (>;). There it forms a layer {fig. 98, h) just beneath their outer 

 wall, and then passes on in the same way to the others, and finally, without leaving 

 Its p(jsUion on the under side of the gastroplu-agma {figs. 74, 77, 0, it pushes its 

 way along the saccules of the genital organs and, diverging there, runs as a distinct 

 layer (o) beneath the exterior wall {i\ oophragma) of each capsule. 



