344 CHARLES LincoLN EDWARDS, 
diameter 166,5 «, with a range from 121,5 to 301,5 «. In the young, 
the mean number of holes is 7 and the size 144 «x 54 u, thus 
demonstrating a growth in these spicules correlated with the general 
srowth of the animal. Among the supporting plates are found 
smaller, slender, curved supporting rods (Pl. 13, Fig. 14), with a 
few perforations and an outwardly projecting crest at the middle. 
b) End-plates. Contrary to SELENKA, 1867, and Cuark, 1904, 
but in agreement with Aykes, 1851, Lürkes, 1857, and MICHATILOVSKIJ 
1902, 1904, I find end-plates present. The pedicel end-plate may. 
be in the form of a single large, rounded, perforated plate with 
jagged edge, about 260 u in diameter (Pl. 13, Fig. 15). The single 
end-plate is characteristic of the young, albeit some pedicels of 
holothurids of this age have a few multiple rods and rosettes. 
In the adult the end-plate is always multiple, being made up 
of several to many rods, smaller rosettes and simple plates. In one 
case 65 of these elements were counted as parts of the end-plate. 
The youngest specimen, and the regenerating pedicel of the 
adult, have the beginnings of the single, or multiple end-plates in 
the form of one, or several, simple, or branched rods. These appear 
before the other spicules develop. Sometimes, particularly in older 
specimens, only vestigeal end-plates are present, or they may be 
completely absorbed. In most cases, except in the very young 
holothurids, the end-plates are difficult to distinguish because of 
the retraction of the pedicel. 
Spicules of the tentacles. — The supporting rods, plates, 
and rosettes are usually crowded in the contracted tentacles. These 
spicules are generally elongated, have knobbed spines and vary in 
size from that of the ordinary body-wall perforated plates in the 
base and main branches of the tentacles to one-half, or one-third 
the size, in the distal twigs of the tentacles. 
The rods may be straight but very often are curved (Pl. 13, Fig. 16) 
in conformity to the tentacle wall. They may be without holes but 
usually have a few perforations. The wider perforated plates 
(Pl. 13, Fig. 17) are more frequent proximally, while distally the 
spieules are simple rods or more or less rosette-like (Pl. 13, Fig. 18). 
Very often the perforated plates have toward the center a 
number of interconnected vertical rods and thin plates forming a 
erest (Pl. 13, Fig. 19). Such sharp-pointed structures, together with 
the spinose ends of many of the other spicules projeeting from the 
surface of the tentacles would assist the holothurid in catching and 
