50 



LUCERNARIJ!: AND THEIR ALLIES. 



mancntly imperforate. At the bases of the tentacles this layer is uninterruptedly 

 contiiuious from one shaft to another, but in the passage it varies largely in thick- 

 ness {jUjs. 54, bO, U), since its proximal side is drawn out into heavy irregular 

 rido'es and bosses (ti), which constitute the main bulk of the large solid, iiUerten- 

 tacular lohtdeH {^\ 103). We should not forget to mention, also, that, as the distal 

 tentacles of a o-voup border close upon the line of junction betv/een the circumoral 

 and aboral parietes of the umbella, the chondromyoplax of the shafts comes to an 

 abrupt terminus at that line ; and, moreover, we would add, that the muscular 

 fibres of these organs project from their basal ends and form a continuous stratum 

 there, lying, like a partition ( fig. 60, Iv), between the umbellar chondrophys ((;) 

 and the cliondromyoplax (?/). Laterally, as we have already pointed out (^ 84). 

 it is continuous with tlie marginal muscular band of the umbella, but is, strictly 

 speaking, homologous only with that part of its border which lies between the 

 termini of the two gclatiniform layers just mentioned. 



101. The (jastmphraiima or lining wall {figs. 54, 60, 90, 91, r) of the tentacles 

 is their thickest layer. Excepting a slight diminution at the apex of the shaft, 

 we find this stratum has a uniform thickness throughout its length until we come 

 to within a short distance of its base. Here a marked change takes place, and 

 what was once an enormously deep wall, altliough composed of a single layer 

 of cells, measuring from one-fifth to one-fourth the diameter of the tentacle, rapidly 

 thins out {fig. 60, *, *') backward to the slender dimensions of the lining wall of 

 the umbella soon after it passes beyond the entrance to the main cavity, in fact 

 before it reaches the ends of the intertentacular lobules, where it is virtually the 

 umbellar gastrophragma (^ 75) . The proximal face of the lining wall of the tentacles 

 is particularly well marked; not so mucli, tliough, by any inherent characters as by 

 tlie dark, irregular pigment granules {fig. 90, e') which crowd into tlie interstices 

 and across the inner ends of its prismatic cells, lying so thickly as to almost tempt 

 one into considering tliem bodily as a distinct stratum. They also serve to light 

 up, by contrast, the boundary of the cavity which they cover, and they are eminently 

 useful in assisting the eye to follow the continuity of this cavity into the umbellar 

 chamber. 



102. The holhwness of the tentacles is unquestionable, and more than that, they 

 openly communicate {fig. 60, ^^) with the main cavity of tlie body. It has been 

 asserted by some naturalists that they communicate only with the lobules at their 

 bases, which have also been described as hollow, and compared to the ampullaceous 

 sacs at the basal ends of the ambulacra of Starfishes.' This is altogether untrue, 

 the lobules being perfectly solid and, moreover, interbasal, instead of being direct 

 prolongations from the tentacles. In the largest, full-grown specimens it is an easy 

 matter to introduce the head of a fine cambric needle between these lobules and for 

 into the cavity of tlie tentacles. It is true that the passage is not broad after the 

 entrance has been fairly made, but it is quite distinct in the young, where the 

 lobules are not developed until some time after the first tentacles appear, and the 

 entrance to the tentacular cavity is quite broadly open ; and the same may be ob- 

 served among the budding tentacles of old individuals. 



' Milne-Edwards and Haime, Hist. Corall. 



