gg LUCERNARI^ AND THEIR ALLIES. 



to an enormous depth (r), amounting to at least twelve to fifteen times its measure- 

 ment in the umbellar camer.e. In this case the tentacles are supposed to be 

 extended to a moderate degree; yet when they are stretched to their utmost 

 capabilities these proportions are not very much diminished. In the anchors the 

 difference is still higher, but there is considerable irregularity owing to frequent 

 indentations in the chondromyoplax, as a longitudinal section {fig. 47, i') of one of 

 these organs shows ; yet it amounts, here and there, to even twenty times as much 

 as the thickness in the more open spaces. In a general way it may be set down 

 as a rule that, at tlie newly forming part of an organ, or where new subdivisions 

 of an or<^an are developing, this wall is thicker than in the older portions {ficjs. 58, 

 8'2, 83). In this layer is situated by far the larger part of the pigment-like matter 

 which gives color to tlie body ; and we may add, without unnecessarily anticipating 

 what properly belongs to the histological portion of this memoir, that the nuclei 

 of the cells are the principal elements in giving depth of hue, while the more 

 widely spread, and scattered interstitial granules produce a general diffuseness and 

 uniformity of tint. 



77. The vlbratile cilia (PI. vii, fig. 74; V\. ix, figs. 98, 99, 100, u; PI. x,fig. 

 109, <j) are truly the next deeply-seated parts of this organization, and although 

 they cannot be included strictly under the head of walls, they at least form appen- 

 dages to these layers, and, therefore, properly deserve mention here, with a state- 

 ment in regard to the extent of surface over whicli they are spread. They occur 

 in all parts of the interior, but are particularly abundant upon the genital saccules 

 and upon one of the flattened sides of the digitiform bodies, but fail entirely on the 

 others, and we believe also in the tentacles. Their structure and especial relations 

 to the cells of tlie wall upon which they are situated will be found set forth, with 

 full details, in the chapter on histology (Ch. VII, 201). 



§ 11. The Muscular System. 



78. General distrihiitioa — A few of the subdivisions of this system have already 

 been mentioned, or in part described, in preceding paragraphs (44, 53, 57, 59, 64), 

 and, therefore, we shall not here enter so fully into all the details necessary to an 

 understanding of their topography and general form as we might otherwise do; 

 but still, not to leave the sequences of our subject disconnected, we shall refer, 

 from time to time, to such of those paragraphs as may be found desirable to com- 

 plete the description. If we except the posterior parietes of the umbella it can be 

 said without exaggeration that every subdivision of every organ of the body is sup- 

 plied with some brancli of the muscular system, and even the excepted region is 

 affected almost directly by one of these subdivisions, for instance, that part of the 

 opsomyoplax which, in the form of a thick rib, trends along the partitions where 

 the chondromyoplax and chondrophys have their only lines of contact (48, 67, 68); 

 or in that part — the doubtful umbello-peduncular region — where the muscular 

 cords emerge from the peduncle and pass obliquely forward into the proximal ends 

 of the partitions (^ 59). In point of relative position the distribution of the various 

 parts of this system is widely diversified; at one place it is either upon, or imbedded 



