GENERAL INTRODUCTION TO THE ZOOLOGICAL SERIES 



OF REPORTS. 



By Sir C. WYVILLE THOMSON, F.KS. 



For a general account of the objects of the exploring voyage of H.M.S. Challenger, 

 and the means by which these objects were carried out, I must refer to the first volume 

 of this Report ; the present introduction is to be understood to apply to the series of 

 zoological volumes only. As, however, the Challenger work in this department was 

 of a very novel and special kind, it may be right to explain somewhat in detail the 

 method and appliances used in procuring and storing the collections ; and the general 

 system under which these have since been made available for scientific investigation, 

 and the results prepared for publication. 



It was a primary object of the Challenger Expedition and one of our special instruc- 

 tions, to determine, as far as lay in our power, the biological conditions of the great ocean- 

 basins. During the short cruise of H.M.S Lightning in the year 1868, Dr Carpenter 

 and I had been able to place it beyond doubt that the use of the ordinary dredge might 

 be carried with comparative ease to a depth of 600 fathoms, and that a numerous and 

 varied fauna existed at that depth; and in the summer of the year 1869, during the 

 second cruise of H.M.S. Porcupine, I found no special difiieulty in sounding, di-edg- 

 ing, and determining the temperature of the water at a depth of 2435 fathoms. Even at 

 this great depth, under a pressure of two and a half tons on the square inch, with a tem- 

 perature close on the freezing point, and probably in utter darkness, animal life was still 

 abundant, and all the principal types of marine invertebrata were represented. 



We were led to believe from previous observations that the average depth of 

 the ocean was not much greater than that of our deepest dredgings, and we were thus 

 forced to the conclusion that there was actually no depth limit to animal life, that the 

 enormous area of the great ocean-basin — extending to over a hundred millions of square 

 miles — had its own special fauna, and that the nature and distribution of that fauna 

 might be brought with comparative ease within the limits of human knowledge. 



