CHAP. I.] INTRODUCTION. 29 



It is right, however, to state that Prof, rieeming 

 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. Erom 

 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 till 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. Eishing the cable up is a 

 delicate and difl&cult 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 



