290 
Holothurla atra 
In the adult the mean number of right canals is 11, Avith a range of 4 — 27 
and of left canals, 12, with a range of 7 — 43. In the young the mean number of 
right canals is 8, with a range of 1 — 13 and of left canals 6, with a range of 2 — 8. 
With the mean number of right and left canals about the same in the adult, the 
left being slightly larger, what asymmetry is present is the opposite to that in 
H. Jioridana. In the yoimg the asymmetry agrees with that of H. floridana but 
is less extensive. In the adult the mean total number of stone-canals is 24, with 
a range of 15 — 70, and in the young, 13, with a range of 8 — 21, not so great an 
age difference as shown in H. floridana. The mean total number in the adult is 
54 % greater in H. floridana. Ludwig, 1889-92, p. 181, gives the range as 10 — 70 
in H. atra. 
The mean greatest length is 10 mm. with a range of 5 mm. — 16 mm. in the 
adult, and 5 mm. with a range of 2 mm. — 8 mm. in the young. 
Thus the number of stone-canals and their length increase with age. The 
mean average length in the adult is 40 ' /^^ greater than in H. floridana. Selenka, 
1867, p. 326, observes that the stone-canals in specimens from the South Sea are 
about \ longer, but not so many as in Florida specimens. 
K. Gonads. 
The gonads and gonaduct agree with those of H. floridana. Of the 12 adults 
7 are male, 2 female, and 3 undifferentiated. Of the 8 young, 6 are undifferentiated 
and 2 have the gonads missing. This undifferentiated state is in harmony with 
the conclusion of Mitsukuri, 1902, p. 18, for Stichopm japonicus, that the first-year 
young and many of the second-year young have the gonads in an undeveloped 
condition. 
Ii. Respiratory Trees. 
Similar to H. floridana. 
M. The Enteric Canal. 
Gardiner, 1901-3, pp. 338 — 40, has studied the important function of H. atra 
and other forms, in reducing coral fragments to sand. The coarser fragments are 
retained in the gut, somewhat reduced in size, while the finer particles are swept 
along the gut, " presumably along its ciliated fold or groove." 
N. Habitat. 
Indian Ocean, Lampert, 1885; Mozambique, Bell, 1884; Madagascar, 
Nossihe, Ludwig, 1883; Aldabra Is., Voeltzkow, 1902; Zanzibar, Selenka, 
1867; Ludwig, 1877, 1887, 1899; Lampert, 1885, 1896; Tumhat I., Baui, 
Lampert, 1896; Amirante Is., Bell, 1884; Darros I., Lampert, 1885, Bell; 
Queriviha (S.E. Coast, Africa), Lampert, 1885; Red Sea, Semper, 1869; Ludwig, 
1887 a; Kossmann, Lampert, 1885 ; Z>;ec^(^a, Lampert, 1885; Ludwig; Laccadive 
