606 CHarLes LincoLn EDWARDs, 
2 vesicles, 3 specimens have besides the primary vesicle, 1 accessory 
vesicle in the left ventral interradius; 1 specimen has the primary 
and 1 accessory in the right dorsal interradius; another has the 
2 vesicles in the left and right ventral interradii, and the last has 1 
in the right dorsal interradius and 1 from the base of the left 
ventral radial canal. Three of the 4 specimens with 3 vesicles 
have besides the primary vesicle, 1 accessory vesicle in both the 
left and right ventral interradii while the fourth specimen has 
1 accessory vesicle in both the left and right dorsal interradii. 
Each of the 5 specimens with 4 vesicles has in addition to the 
primary vesicle, one in both the left and right ventral interradii 
and the fourth accessory vesicle in the right dorsal interradius while 
the holothurid with 5 vesicles has them similarly located but with 2 
in the last named region. One specimen has the origin of the pri- 
mary Polian vesicle spreading over the neighboring radial regions. 
Another holothurid has no primary Polian vesicle but instead 60 little 
sacs from 0,2—1,2 em long arising from the ring-canal and the bases 
of the radial canals. Each little vesicle has 1 or more round white 
cysts about 1 mm in diameter and filled with some micrococeus. 
Such cysts occur also in other specimens. 
The mean length of the primary Polian vesicle in the adults 
with 1 vesiele is 19 cm with a range from 9—36 cm. When there 
are several Polian vesicles some, if not all, are shorter than the above 
mean. In the young holothurids (with the body under 3—4 cm 
long), the mean length of the Polian vesicle is 2,6 cm and thus it 
is evident that in this species the size of the Polian vesicle is 
correlated with age, while the variation in number is not. 
Stone-canal. — As noted by Lupwıc, 1881, LAmPErT, 1885, 
CLARK, 1902, and Epwaros, 1907, there are numerous stone-canals 
which in accord with LAmrerrT can be divided into 2 classes. These 
I will call the prineipal and accessory stone-canals. The prineipal 
stone-canal has a mean length of 4,9 mm with a range from 6—12 mm 
and the usual median dorsal location. The accessory stone-canals 
have a mean number of 66, with a range from 4—140, and a mean 
length of 21 mm with a range from 1 mm or less to 6 mm. As 
my earlier paper (1907) shows, some of these stone-canals are bifid 
and some, trifid. 
The madreporite of the principal stone-canal is spherical in 
form in a majority of cases but frequently it is either irregular, 
elongated, or lens-shaped, and has a mean diameter of 1,2 mm with 
