280 Holothiiria atm 
TABLE XXXII. 
b. Distribution of Papilla k around the Anus. 
In Groups 
Age 
Number of Groups 
Indefinite 
Tctal 
0 
1 
2 
s 
J^ 
5 
Adult ... 
0 
0 
0 
0 
1 
4 
7 
12 
Young 
2 
0 
0 
0 
0 
3 
3 
8 
Table XXXII. shows that all of the adults have anal papillae. In 42 ° the 
papillae are in groups, and in 58 "/^ they arc indefinitely distributed. Of the 
8 young, two have no anal papillae, three have 5 groups and three have the 
papillae indefinitely distributed. 
E. The Body-wall. 
a. Thickness in mm. 
(Determined as in H . floridana, p. 256.) 
TABLE XXXIIL 
Adult 
Young 
Number of Specimens 
Mean 
Standard Deviation 
Coefficient of Variation ... 
Range of Variation 
12 
1-717+ -173 
•886+ -122 
51 -'599 + 7^104 
•6—4-0 
8 
1-575+ -052 
-217+ -037 
13-746 + 2-318 
1-0—1-5 
The mean thickness of the body-wall is only -14 mm. greater in the adult than 
in the young. The range in the adult shows one 4 mm. thick, but in most cases 
it cannot be said to grow much thicker with age, in which it differs decidedly from 
H. floridana (cf. p. 256). In H. floridana the mean thickness of body-wall is 
2-4 greater than in H. atra. Thus the body-wall in H. atra is comparatively thin, 
soft and flaccid while in H. floridana it is nearly always much thicker, and even 
when not thicker, it is usually hard and firm, especially in the adult. Lindmann, 
1899, claims that in the changes of consistency in the body- wall from hard to soft 
the albuminous element of the slime-secretion plays the most important part. 
While this may be true of the physiology of these tissues, yet I should account for 
the specific difference above noted in the greater thickness and the much larger 
number of spicules found in the body-wall of H. flo7'idana (cf. p. 256). The 
standard deviation, especially in the young of H. atra, is very small. 
