GENERAL INTRODUCTION TO THE ZOOLOGICAL REPORTS. 



33 



The Nature and Distribution of the Fauna of the Deep Sea. 



The special character of the fauna of the deep sea, so far as it is at present known, 

 the sources from which it may have been derived, and its relations to the fauna of 

 shallower water and of the fauna of past periods of the earth's history, will be discussed 

 in detail in the summary of general scientific results, which will form the last volume 

 of this report ; it may be convenient, however, to give in this place a preliminary 

 sketch of its general nature and scope ; that the reader may form some idea of the rela- 

 tions, extent, and relative importance of the groups treated in the following memoirs, 

 and of the conditions under which they severally occur. 



The Absence of a Depth-Limit to Life. — The most prominent and remarkable biological 

 result of the recent investigations is the final establishment of the fact, that the 

 distribution of living beings has no dejath-limit, 

 but that animals of all the marine invertebrate 

 classes, and probably fishes also, exist over the 

 whole of the floor of the ocean. 



My present impression is, that although life is 

 thus universally extended, the number of species 

 and of individuals decreases after a certain depth 

 is reached, and that at the same time their size 

 usually diminishes. This latter observation is 

 not, however, true for all groups ; a peculiar 

 family of the Holothuridea, the Elpididse (fig. 

 13), very widely distributed in deep water and 

 found at the greatest depths, maintain the full 

 dimensions of the largest of their class, and even 

 exhibit some forms of unusual size. On two 

 occasions in the North Pacific we brought up, 

 from depths of 1875 and 2900 fathoms respect- 

 ively, a species of Monoccmlus, a tubularian 

 hydroid allied to Corymorpha, a giant of its fic i3-^«-'««/«^<«^'». Theei. one of the Eipidito. 



order, with a stem upwards of 7 feet high, and a head nearly a foot across the 

 crown of expanded tentacles. 



Of the value of our present impressions on any question relating to the nature, or the 

 relative abundance, or the relative size of the animals constituting the fauna at depths 

 approaching 3000 fathoms, I am by no means sure. Using all precautious, and with 

 ample power and the most complete appliances, it is extremely difficult to work at such 



