xii THE VOYAGE OF H.M.S. CHALLENGER. 



difficulty in deciding which animals were dredged from the bottom and 

 which were caught by the instruments in the surface or subsurface waters. 

 With some Fish, Crustaceans, Medusse, and other groups, however, there is 

 considerable difficulty ; in these cases the organisation is often a guide, and 

 the specialist who has made a careful study of the group to which the species 

 belongs, is best able to form an opinion as to the depth at which the 

 specimens were probably captured. These circumstances should therefore 

 always be borne in mind when the depths at which animals have lived are 

 being discussed, and only after careful consideration should it be inferred that 

 they were procured at the depths ascribed to them in the lists. 



We desire on our own behalf, and on that of the members of the 

 Expedition generally, to offer most grateful thanks for the liberal hospitality and 

 ready assistance we received in all parts of the world, not only in the British 

 Colonies but also in Foreign Countries. It has not been possible to refer in 

 every instance to those who extended a friendly welcome to members of the 

 Expedition and added so much to the pleasure of the Cruise, but the 

 remembrances of many incidents and friendly acts appear, to the members of 

 the Naval and Civilian Staffs who survive, to grow brighter rather than more 

 dim with the lapse of time. 



