CHAP. I. ] INTRODUCTION. 29 
It is right, however, to state that Prof. Fleeming 
Jenkin’s notes refer to only one or two species, and 
especially to Caryophyllia borealis, as attached to the 
cable at a depth of upwards of 1,000 fathoms. From 
this depth he took examples of Caryophyllia with his 
own hands, but he suspects that specimens from the 
shallower water may have got mixed with those from 
the deeper in the series in the possession of M. 
Mangon, and that therefore M. Milne-Edwards’ list is 
not entirely trustworthy. 
Up to this time all observations with reference to 
the existence of living animals at extreme depths had 
been liable to error, or at all events to doubt, from 
two sources. ‘The appliances and methods of deep- 
sea sounding were imperfect, and there was always 
a possibility,from the action of deep currents upon 
the sounding-line or from other causes, of a greater 
depth being indicated than really existed; and again, 
although there was a strong probability, there was 
no absolute certainty that the animals adhering to 
the line or entangled on the sounding instrument 
had actually come up from the bottom. They might 
have been caught on the way. 
Before laying a submarine telegraphic cable its 
course is carefully surveyed, and no margin of doubt 
is left as to the real depth. Fishing the cable up isa 
delicate and difficult operation, and during its progress 
the depth is checked again and again. The cable lies 
on the ground throughout its whole length. The 
animal forms upon which our conclusions are based 
are not sticking loosely to the cable, under circum- 
stances which might be accounted for by their having 
been entangled upon it during its passage through the 
