C. L. Edwards 
273 
greater number of canals on the right side, while only 15 of the adult and 9 7^ 
of the young have the number greater on the left side, and 1 "/_, of the adult and 
lo 7o of the young have the same number on both sides. So Ludwig must have 
made his counts from the less frequent individuals in which the number on the 
left is greater. 
In both adult and young the standard deviation and range of variation are 
greater for the right canals. 
In the adult the mean total number of stone-canals is 37, with a range of 
5 — 149, and in the young 10, with a range of 2 — 25, demonstrating the great 
increase in the number of these organs through continued budding as the 
Holothurid grows. Specimen 08 with the large number of 149 stone-canals is 
exceptional, but 37 /^^ of the adult have more than 40 stone-canals. This should 
be particularly noted since Ludwig, 1889-92, p. ISl, mentions H. mexicana as 
having a range of from 11 — 40 stone-canals. Lam pert, 1885, p. 85, gives them as 
very numerous in two specimens of H. mexicana. 
The mean greatest length is 8 mm. with a range of 3 mm. — 21 mm. in the adult 
and 3 mm. with a range of 1 mm. — 7 mm. in the young. To determine the average 
length of all the canals of an individual the mode was selected by inspection and 
measured. The mean average length is 5 mm. with a range of 1"5 mm. — ID'S mm. 
in the adult and 3 mm. with a range of 1 mm. — 6 mm. in the young. Thus the 
number of stone-canals and their length together with their standard deviations 
increase with age. 
L. Gonads. 
The gonads are branched and form a tuft to the left side of the dorsal 
mesentery. The gonaduct opens dorsally just behind the circlet of tentacles. In 
most individuals, the sex cells mature in July and August (Edwards, 1889, p. 37). 
Of the 73 adults, 35 are male, 35 female, 1 undifferentiated and 2 with gonads 
missing. Of the 45 young, 14 are male, 12 female, 12 undifferentiated and 7 with 
gonads missing. 
M. Respiratory Trees. 
Each of the two main stems of the respiratory tree has short branches whose 
median terminal twigs are intertwined with the blood-vessels of the rete mirabilo. 
N. The Enteric Canal. 
The enteric canal is in three loops supported by a mesentery attached to the 
body-wall. It is large, with delicate wall and always crowded full with calcareous 
sand. At the posterior end is the expanded cloaca, its tough wall being attached 
to the body-wall by numerous small muscles. 
Biometrika vi 36 
