208 
immature at this size, the gonads only being fully developed in 
specimens c. 8 mm long. 
The Atlantic form is pale yellow in colour, the Hawaiian is 
dark chocolate-brown. — From an anatomical point of view these 
two species are not differing in many points. This was not likely 
either as the Holothurians belonging to these genera are of a very 
uniform type. — I have compared specimens of nearly equal size 
and have found the tentacleampullae to be larger and darker pig¬ 
mented in the Hawaiian form than in the Atlantic. The number 
of Polian vesicles is in most cases 2 for the Hawaiian, 3 for the 
Atlantic species, but this is not quite constant, as I have found 
specimens of the latter species with only one, and a specimen from 
Hawaii with 3 vesicles, the third being very 
small. 
A very distinet difference is afforded by the 
Cuvierian organs, which are in the Atlantic 
form discharged in the form of long thread- 
fine bands, as noted by Crozier; in the Ha¬ 
waiian form Dr. Mortensen has observed 
that when the animals are irritated they dis¬ 
charge the Cuvierian organs in small bits, re- 
calling „vermicelli soup“. The calcareous ring 
affords the best distinguishing character of the 
two species; in the works of Fisher and 
Ludwig pieces of the calcareous ring are 
figured, the differences between the two spec¬ 
ies thus being clearly shown. I have figured pieces of the calc¬ 
areous ring from the present material. The ring of the Atlantic 
form (Fig. 5 a) is very thin and low. When treated with hypo- 
chlorite of sodium the ring is easily isolated without losing its 
characteristic form. The ring of the Hawaiian form (Fig. 5 b) is 
thick, high and robust. After very short treatment with hypochlor- 
ite of sodium the losely united spicules of the ring are set free 
and the ring is destroyed, long before the organic substance has 
been dissolved. Also by ordinary preparation with a scalpel the 
little thin ring of the Atlantic species is far more resistent than 
the thick, robust ring of the Hawaiian form. 
The deposits in the skin show a well marked difference (Figs. 
a. 
Fig. 5. Part of the calcar¬ 
eous ring of Actinopyga 
parvula (Sel.) (a) and A. 
difficilis (Semper) (b). 8 /i. 
