NATURAL HISTORY OF AFRICA. 473 
the tropical seas, and on the coasts of Africa, is of- 
ten seen sailing on the surface of the ocean, by- 
means of a particular organ which it uses as a sail, 
and hence is named by the French le petite galere, 
and by English mariners the Portuguese sailor. 
The red coral, (Corallium rubrum, Cuvier,) 
so well known as an article of trade, is fished up 
oil the coasts of Tunis, and in the waters of the 
Red Sea. It grows much slower than the madre- 
pores, and never occurs in such masses. It is 
found at different depths, and it is remarked, that 
light exerts a powerful influence on its growth. 
Thus, at a depth of from three to ten fathoms, it 
grows one foot in eight years ; at the depth of from 
ten to fifteen fathoms, the same length in ten years; 
at the depth of one hundred fathoms, same length 
in twenty-five or thirty years ; and, at the depth 
of one hundred and fifty fathoms, the same length 
in forty years. It is also remarked, that in gene- 
ral the colour of the coral is deeper and richer in 
shallow than in very deep water. The coral of 
Barbary is not reckoned so fine as that of Italy or 
of France. 
Many species of madrepores are found on the 
African coasts, from N. L. 30° to S. L. 30°; 
but it is not true, as some maintain, that the 
same species are distributed throughout the whole 
range of latitude just mentioned ; on the contrary, 
each species has its determinate place of abode, 
