286 
Holothnria atra 
The absence of a sucker is characteristic of the papilla, and since 59 7o of the 
dorsal appendages lack this organ they may be considered as papillae. 
c. End-plates. 
In 12 (5'9 of the dorsal appendages there is no trace of an end-plate, a 
condition which only occurs in 1 7^ of the dorsal appendages of H. floridana. In 
2 (1 °/^) the end-plate was not determinable. 
TABLE XXXVI. 
Diameter of End-plates in /x. 
Dorsal 
Ventral 
A 
B 
C 
D 
E 
A 
B 
C 
I) 
Frequency 
89(46-8%) 
70 (.36-8%) 
22(11-6%) 
8 (4-3%) 
38(71-7%) 
10(18-9%) 
3(5-7%) 
1(1-9%) 
1(1-9%) 
Mean 
450-00 
283-652 
169-349 
107-727 
78-750 
669-473 
339-000 
175-001 
105-000 
60-000 
+ 3-778 
+ 2-262 
+ 3 -.367 
+ 4-979 
+ 10-687 
+ 11-720 
+ 7-286 
Standard 
52-812 
27-858 
23-412 
20-879 
97-671 
54-950 
18-710 
Deviation 
+ 2-670 
+ 1 -600 
+ 2-381 
+ 3-521 
+ 7-557 
+ 8-288 
+ 5-152 
Coeflicient of 
18-619 
16-450 
21-733 
26-512 
14-589 
16-209 
10-691 
Variation 
± -941 
± -945 
±2-210 
±4-471 
± 1-129 
± 2-445 
±2-944 
Range of 
Variation 
225—420 
105—210 
60—135 
60-120 
465—825 
240—405 
150-195 
In the bivium there is only one end-plate of Type A, with a diameter less than 
that of the smallest variate of this type in the trivium. Types A, B and C are 
larger and more variable in the trivium, and each of the vestigeal rosette-like 
end-plates, D and E, is found but once, while dorsally D occurs in 12°/^ and E in 
■i of the cases. 
Comparing Table XXXVI. with Table XXI. it is seen that in H. floridana the 
mean diameters of all the types are larger, while in H. atra only one dorsal end- 
plate is large enough to be placed in Type A. So, from a consideration of the end- 
plates, it is obvious that the evolution by degeneration of the papilla from the 
primitive pedicel is much more marked dorsally in both species, and that all over 
the body it has proceeded decidedly farther in H. atra than in H. floridana. 
Selenka, 1867, p. 326, notes that specimens from the South Sea have the end-discs 
\ smaller than those from Florida. 
d. Supporting Rods. 
Dorsal. 
In the bivium supporting rods are absent in 146 (71*6 7o) of the appendages, 
present in 82 (15-7 7o) not determinable in 26 (12-7 7o)- I'he description 
given on p. 266 covers the dorsal supporting rods of this species. 
