INTRODUCTION. 
€—— 
My connection with the thalassographie work of the Coast 
Survey dates back to 1849, when, as a boy, I accompanied Pro- 
fessor Agassiz in his cruise on the * Bibb " off Nantucket, and 
afterward, in 1851, served as aid on his survey of the Florida 
Reef. More than twenty years later I returned to this line of 
study, in a report on a part of the collections made by Pourtalés 
in the “ Bibb ” in deep water in 1867—68, and since that time I 
have been engaged, with little interruption, more or less directly 
in deep-sea work. It was therefore natural that I should accept 
the invitation given me in 1877, by Mr. Patterson, the Superin- 
tendent of the Coast Survey, to continue, under its auspices, the 
work in which I had begun my biological studies. If at times 
the physical difficulties encountered were somewhat discour- 
aging, it was a great pleasure to find that my professional train- 
ing as an engineer not only contributed in no small measure to 
the success of the expedition, but also increased my interest 
in the many problems of deep-sea explorations. 
The field of work opened to naturalists by thalassographic 
surveys is of the greatest importance. The materials collected 
throw a flood of light on our knowledge of the conditions of 
animal life in deep water, and promise the most important gen- 
eral conclusions on terrestrial physics and on geology. Fasci- 
nating as has always been the study of marine life, this interest 
has greatly increased since we haye found the means of reach- 
ing the abyssal fauna. Light has suddenly been shed on many 
vexed problems concerning the geographical distribution of 
animals and plants and their succession in time from former 
geological periods to the present day. New notions of geologi- 
