DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
789 
Figs. 190 to 193 illustrate the most usual succession of the teeth. The first to 
develop are those of the ventro-lateral chambers (fig. 190). These are often enor¬ 
mously elongated, especially in the posterior parts of the disc, and they remain for a 
long time distinctly longer than the others, as may be seen in fig. 193. After a 
considerable interval they are followed by the calyx-tooth of the dorsal chamber 
(fig. 191). The lateral teeth appear nearly simultaneously; but so far as I have 
observed, the median-lateral teeth usually precede somewhat the dorso-lateral. This 
is sometimes quite decided (fig. 192) ; but in a few cases the dorso-lateral teeth are 
first to appear. According to Kolliker this is the rule, and he states that when 
five teeth are present, the missing teeth are always those of the median-lateral 
chambers. The ventral chamber very rarely develops a tooth. In younger buds, 
when all of the teeth are formed, they usually increase pretty regularly in length 
from above downwards, and this gradation is more marked usually in posterior parts 
of the disc. In later stages, the difference gradually becomes less, until the teeth 
are of nearly equal length. In the rare cases of the appearance of a ventral tooth 
this is always smaller than the others. The calyx-teeth vary greatly in length in 
different colonies. We note, finally, that the calyx-teeth are usually all formed 
before the tentacles appear, whereas the reverse is true of the primary polyp. 
It is surprising to find this regular succession in the appearance of the calvx-teeth, 
which must be structures much younger, phylogenetically, than the tentacles. It may 
perhaps depend upon the circumstance that the polyps are in early stages placed side 
by side, so that the upper and lower calyx-teeth are more directly exposed to the 
environment. This does not, however, account for the absence of a tooth on the 
ventral chamber, and in our ignorance of the functions of the teeth in early stages, it 
is useless to speculate on the matter. In the mature bud the teeth probably serve 
as an armature for the mouths of the polyp-cells, since they are then stiffened with 
spicules and must form an effective defence. They can hardly perform such an office, 
however, in the young buds and in the zooids, though their early and ample develop¬ 
ment in both these cases indicates that they must perform some function. The very 
brilliant and beautiful phosphorescence of the colony appears to have its principal 
seat in the calyx-teeth of the young buds ; but this can hardly throw any light upon 
their function. 
Whatever be their function, the sequence in the development of the calyx-teeth 
seems to stand in no relation with the definite succession of the tentacles in some 
Zoantharia, but is dependent upon some special unknown conditions peculiar to the 
Renilla colony. 
b. Development of the tentacles. 
The formation of the tentacles agrees entirely with that of the tentacles of the 
primary polyp, and calls for no special remark. They make their appearance 
simultaneously, after the formation of the calyx-teeth, as conical outgrowths of the 
MDCCCLXXXIIl. 5 I 
