256 
Holothnria Jloridana and Holothuria atra 
TABLE XVII. 
Determined by measuring in mm. the thickest and thinnest places 
along a ventral incision and then taking the average. 
Adult 
Young 
Number of Specimens 
Mean 
Standard Deviation 
Coefficient of Variation ... 
Range of Variation 
62 
4-144+ -195 
2-274+ -138 
54-876+ -332 
1-0—13-0 
44 
1 -495 + -084 
-827 + -059 
5-527+ -397 
•1—3-0 
Naturally some individuals will die with the body-wall much more contracted 
than the average, and others with it much more expanded. Thus in 56 the body- 
wall is quite uniformly "thin" ("S mm.— I'O mm. thick) and in this one character 
the specimen is similar to H. atra. 
G. Calcareous Spicules of the Body--wall. 
These spicules are of three classes ; tables, rosettes and perforated plates. 
They are not always distributed evenly throughout the body-wall but often in 
heaps and groups, which in some cases may be due to greater contraction in the 
regions where they occur. In general the spicules are more numerous in the 
trivium. At least in the young the spicules are being developed constantly, so 
that a more or less complete series of stages illustrating their development may be 
secured. The data were obtained from pieces of the body-wall of 2 or 3 sq. cm. 
area taken from near the middle of the body, cleared in dilute potassium hydras 
and then, after dehydration by the alcohols, mounted from cedar oil into balsam. 
a. Tables. 
The tables in H. Jloridana are like those of H. atra and so in the following 
general description of their development, structure and variation no attempt is 
made to keep separate account of H. Jloridana and H atra specimens. The tables 
studied did not lie near any appendage and so unquestionably belong to the body- 
wall. They are found in the superficial layer of the dermis. 
1. Development of the Table. 
The developmental series represented by PL IV., Figs. 42 — 49, was selected 
from many individuals during the progress of this study. As shown by Diiben 
anil Koi-en, 1844, this spicule begins as a cross-shaped body or as better expressed 
by Ludwig, 1889-92, pp. 45, 56, as a short rod with forked ends (Fig. 42). At the 
proximal end of each prong a vertical rod arises (Figs. 43, 44). The end of each 
