LUCE TIN A RLE AND THEIR ALLIES. 89 



pletely, but immediately beyond, however, it expands laterally and diverges into 

 the main fold. By plunging through the circumoral floor, and focussing up and 

 down upon the saccules, we learn that the follicles do not develop at an equal rate 

 throughout the cavity into which they open, but on the contrary originate progres- 

 sively and grow at a corresponding rate. This is clear enough if we compare those 

 which lie on a level with the aperture of the saccule with those which are placed 

 at more distant points ; the former appearing as scarcely more than shallow 

 depressions {fi<J- 11) in the inverted wall, wliile the latter are to be recognized as 

 inicquivocal pouches {fig. 72, s") Avith a rounded contour and a narrow aperture. 

 That all of the follicles do not originate at once is proved by a glance at the next 

 figure {fig. 73) which we shall use to illustrate the series. 



178. We now present the last phase of development of the saccules that we are 

 in possession of; and we think that it is far enough advanced to connect the ear- 

 lier stage of the organ with its full grown condition. There is really nothing new 

 in point of character in the specimen {fig. 73), and it diff'ers from the previous one 

 merely in the greater size and jnore abundant follicles (.f") opening into the general 

 cavity of the saccule. Up to this period no trace of eggs nor of spermatic parti- 

 cles has been met with, neither, unfortunately, are we able to furnish any informa- 

 tion in regard to the mode of origin of the reproductive material. The size of the 

 saccule before us measures from one-fourth to one-third the diameter of full grown 

 ones ; and the follicles are as yet far less in number, amounting at most to only forty 

 or fifty. The latter are a little larger than those of the last stage {figs. 71, 72), and 

 press closely against tlie outer wall of the saccule. 



179. The Cho)i(Iro'mi/02)Jax. — We return now to the more legitimate objects of 

 this section, and take up in turn the successive layers of which the body is com- 

 posed, as far as we have the material to work with. We find at this stage of 

 growtli the first tolerably clear dificrcntiation of the clionilronnjojiJax from the mus- 

 cular layer. This is seen best in the oldest tentacles {fig. Tj*), A, ?/r), and with 

 ratlier more difficulty in the circumoral region. In either case it is not more tlmn 

 two-thirds as tliick as the outer and inner walls in tlie same place, and from two to 

 three times thicker than the mviscular layer. In the ancliors {fig. 32) it has a 

 much greater depth, amounting to from three to four times that of the outer wall. 

 As yet it appears to be perfectly homomorphous, a mere structureless, chondroid 

 stratum. This is all we have to say, liere, of tlie chondromyoplax. Tlie descrip 

 tion of its origin and mode of development belongs more properly to tlic histology 

 of the layer. 



180. The Chondrophijs. — This layer is at least twice as deep in the umbella as 

 the diameter of the oldest tcnitacles of the individual now in hand. Its histo- 

 logical elements are much more delicate than in the last {iliase, as far as it may be 

 estimated from that part of it in the peduncle of the latter ; and it is diflbrentiated 

 into two distinct strata {fig. 58, c, c"'). The outer stratum {(■'') is comparatively 

 thin, not more than half tlie thickness of the outer, al)oral wall immediatc^ly over- 

 lying it. Moreover, it, conjointly with the muscular laytn-, forms the partition 

 which lies between the great mass of the chondropliys {(■) and that part of the 

 chondromyoplax which is in the tentacles. Tlie inner .strattuu constitutes nine- 



12 March, 1878. 



