LUCERNARI.E AND THEIR ALLIES. 19 



and most distant opposite the corners of the proboscis, since the areas continuous 

 with the buttresses are the least depressed (39). From the hitter points the faces 

 in question approximate each other along two diverse lines, one trending in the 

 direction of the partitions, where they are conjoined, and the other ruiniing to the 

 margin of the umbel, at which place they combine to form a common border. 



44. The phydojnomy of the anterior face of the umbel is still further affected 

 by the location of the subdivisions of the muscular system. This system is much 

 more intensified and conspicuous in the regions adjacent to the partitions (v') than 

 in the intervening areas, but in both localities it may be recognized by numerous 

 ribbon-like bands {m) which extend parallelwise from about the base of the 

 proboscis to the periphery of the umbel. The subdivisions are divided into two 

 sets, of which there arc four more prominent subdivisions opposite the flanks of 

 the proboscis, and four others regularly alternating with these and ruiniing directly 

 from the buttresses (<^'') of the same organ. These eight subdivisions are not 

 apparently in contact with each other, but seem to be separated by the intervention 

 of eight other subdivisions of another system of organs. The latter, the genitaUa, 

 are dark, triangular, flat masses ( .), which present the appearance of a pavement- 

 work as seen through the walls, and extend, one by one, from the sides of the 

 buttresses to the tentaculiferous corners (4-^) of the octagon. The absence of the 

 muscular system over these triangular areas is only apparent, and is obscured by 

 the darkness of the underlying mass. Finally there is a narrow ribbon (»<') of 

 muscle which borders the front face of the vunbella, but does not extend as a 

 distinct band over the corners where the tentacles are situated. By the action of 

 the muscles the front face of the umbel is largely modified at times, either by the 

 contraction of the fainter, weaker set, in such a way that the whole area opposite 

 each of tlie buttresses, with the latter included, is thrown forward into a strong 

 narrow ridge, and the adjacent triangular masses of pavement-work are approxi- 

 mated so as to touch, of even overlap each other {fi<j. 3), or at other times the 

 stronger muscles narrow the sunken areas in which they lie, until they become 

 quite restricted in extent and deeper as a whole in an antero-posterior direction, 

 and simultaneously the intertentacular margin is shortened and rendered more 

 deeply sinuous {fig. 22). On the whole it may be said that the entire floor of this 

 face is quite thin and highly expansible and contractile. 



45. The jMsterior face {figs. 17 and 66) of the umbella is quite simple in con- 

 figuration. Being coincident at its margin with that of the front face, it is 

 bordered by the same appendages, i. e., tentacles and adherent organs, and by its 

 semi-transparency allows a tolerably clear view of the partitions {^-) and the dark 

 triangular bodies (Z). Its thickness is very marked in contrast with that of the 

 anterior face, nor does it ever appear to become wrinkled or folded to any dis- 

 tinctly appreciable extent. This may be readily accounted for, since Ave know that 

 the bulk of it consists of a highly resilient, gelatinifornl substance, continuous with 

 that in the peduncle (58). Contrasted, then, with the other face, it might well be 

 described as rigid. Opposite the four partitions, however, it is more or less slightly 

 impressed with a shallow, broad, longitudinal furrow, which scarcely attracts 

 attention unless looked for. That it is capable of being compressed or bent is 



