C. L. Edwards 
249 
The mesentery is attached at the junction of the dorsal interradiaie with the 
left dorsal radiale in 10 cases (15, 28, 35, 41, 45, 66, 68, 70, 73, 89) and with the 
right dorsal radiale in 1 (98) ; to the left side of the dorsal interradiaie in 33, 37, 
and to the right side in 34; slightly to tlie left of the mid-line in 19, 20, 77, and 
to the right of the mid-line in 113. The attachment is very broad for about 
1 cm. in 40. In 37 the dorsal interradiaie is fused with the right dorsal radiale. 
One would anticipate that the displacement of the tentacles should be in the 
opposite direction to the displacement of the mesentery found in 14 of the above 
cases. Such a relation indeed is present in 11 of the 14 specimens. While the 
mean, in adult and young, is about the same, there is^ greater range and greater 
variability in the adult than in the young. 
b. Number of Tentacles. 
TABLE IX. 
Adult 
Youug 
Number of Speci m en s 
Mean 
Standard Deviation 
Coefficient of Variation . . . 
Range of Variation 
73 
19-709-1- -064 
•808 + -045 
4-099+ ^229 
16—22 
4.5 
19 -756 -t- -064 
-642 -f- -025 
3-229+ -229 
18—21 
Variation in the Number of Tentacles and the Relation of those Present to 
the Normal Symmetry. 
Adult and young are tabulated separately but under this particular head they 
are treated as one group. Among the 30 varieties there is a decided tendency 
to reduction in the number of tentacles, since 23 individuals (76"6 ° j^) have less 
than the norm of 20 tentacles. It is well known that holothurians may lose one 
or more tentacles by accident, hence this excess in individuals with less than the 
norm probably represents such losses rather than congenital variation. This in- 
terpretation is also justified by the fact that in many cases of deficiency of 
tentacles the normal number, 20, of ampullae, is present. 
Of the 12 cases in the 19 tentacle class, 9 (75 7o) have the tentacle absent in 
the trivium. Of the 10 cases in the 18 tentacle class, 3 lack the 2 tentacles in the 
trivium, 1 in the bivium, 4 lack 1 tentacle in each region and 2 are not deter- 
minable. Of the 23 cases in all, 15 (65 7o) have the tentacle deficiency in 
the trivium. 
Holothurid 5 with 16 tentacles, lacks the 4 of the left ventral interradius, ^2, 
v\ from the left ventral radius and ^2, II from the mid-ventral radius. In the 
Biometrika vi 32 
