LUCERN ARIyE AND THEIR A LLIES. 29 



or, in other words defining the meaning of the term, it is the face mnsctdar layer ; 

 and to it are due all the muncroiis changes of physiognomy and attitude which 

 the umbella of this creature exhibits from time to time. It has the same extent both 

 anteriorly and posteriorly, and over the tentacles and anchors, as the wall which 

 it underlies, but, unlike the latter, its borders terminate abruptly, without 

 connection with any other stratum. Its continuation witli the peduncular cords 

 has already been described in a previous paragraph (59). The peripheral margin 

 {figs. 61, 62, /r') is not exactl}'* coincident with that of the opsophragma, as it 

 terminates at this place in a peculiar manner, which will be described hereafter in 

 the section (§ 11) on the muscular system. As it is one of the layers which add 

 to tlie bulk of the body and serve as partitions between other strata, it is desirable 

 to mention certain features here which distinguish it from those on each side of 

 it, or which serve to assist in defining the boundaries of adjacent strata. In 

 general terms it may be said to be even thinner than the opsophragma, at its least 

 depth, but, unlike that, it does not vary in thickness over considerable areas, and 

 yet there are regions, quite limited it is true, within wliich it appears to attain 

 a great thickness. But these are rather to be considered as deep folds {figs. 61, 

 62, ?/i\ ?H"), and correspond in position to those places where the muscular system 

 seems to be composed of parallel bands or cords (see ^ 44). After what has 

 been said above, it will hardly seem necessary to remark that it totally fails in the 

 region of the ectophragma {*\ 6-3) ; but we must not omit to add that anotlicr part 

 of the same system, in another forni-j-the peduncular cords (^ 59) — appears in 

 that portion of the body, but, in this genus, dpcs not form a distinct layer. 



65. The cliondromyopJax (PI. in, fig. 33 ; PI. iv, figs. 44, 47, 47% 48 ; PI. v, 

 figs. 53, 54, 60; PL vi, figs. 61-64;' PI vii, figs. 7*4, 77, 82, 83; PI. viii, figs. 

 90, 91 ; PI. IX, fgs. 98, 100, h to //), or the muscido-gclatiniform layer as we 

 have called it in another paper,^ and the elioudropliys, or the gclatluiform layer, 

 constitute, together, by far the greater bulk of tlie solid material of the body. 

 They are the jelly-like substance which renders the innbella of the medusiforra 

 Acaleph so massive. Among the Ilydroida it is the cJiondrophys Avhicli forms the 

 distinctive feature of the mcdusa-cephaloid, and the only thing which the hydro- 

 cephaloid variety of this morph has not, the choitdmmyoplax being altogether 

 absent in neither (Part XI). Among tlie Strobiloida, tlie medusa-cephaloid 

 possesses both of these layers, while its hydra-cephaloid — tlie Scypltostnma — has 

 only the cliondromyoplax (Part ILl,' Aurelia). Tlie latter will here receive our 

 first attention. The most notable feature, besides the thickness of the chondro- 

 myoplax and its excessive extensibility, flexibility, and compressibility, is the 

 striation which traverses it froifi surface to surface ; yet we do not pretend to say 

 that by this the layer may be distinguished from all others, for a similar striation 

 prevails in the chondrophys {% 69), but we claim that it alone, among the walls of 

 the front parietes of the umbella, possesses this characteristic, and by means of it 

 may be traced to its utmost limits with a comparatively low magnifying power. 

 This layer iniderlics and is coextensive with the opsomyoplax (64), and in fact we 

 cannot well persuade ourselves that it is altogether a separate stratum from the 



' " Luceniiu'ia the Cccudtypo," etc., ut sup. 



