208 I'liiversity of Calif o)-nia Publications in Zoologij [Vol. 15 



INTRODUCTION 



Experience gained througrh the marine explorations of the Scripps 

 Institution demonstrates that variations in hydrographic as well as in 

 many strictly biological conditions decidedly influence the vertical 

 and horizontal movements of marine organisms, their abundance at any 

 particular time and place, and many aspects of their life-histories and 

 relations to one another. In fact, such hydro-biological relations are 

 too complex, by far, to be discovered without numerous and detailed 

 hydrographic observations corresponding in time and place to the 

 biological ones. Not only is this true, but the variability in tempera- 

 ture and salinity, not to mention that of many other elements, is so 

 great and its causes so complex as to demand much more continuous 

 investigation than ha.s been thus far possible. With these considera- 

 tions in view, the Scripps Institution has temporarily discontinued its 

 systematic plankton exploi'ations, and, instead, is devoting time and 

 energy to devising methods and equipment more suitable for conduct- 

 ing the more intensive researches required. It seems probable, there- 

 fore, that the next series of investigations will differ in many important 

 respects from those already made. For this reason, together with the 

 fact that a summary of all the hydrographic re.sults is ready for the 

 press, it is desirable to bring the publication of our crude data to date. 



The present paper, therefore, includes the field data relative to all 

 hydrographic and biological collections made since 1912. Since that 

 time, no soundings, gas analyses, or current-meter observations have 

 been made, and the hydrographic data relate entirely to temperatures 

 and salinities. Similarly, dredging and trawling have been tempor- 

 arily discontinued, except for museum and supply purposes; hence, 

 the biological data relate only to plankton collections. 



The apparatus, methods of collecting, methods of laboratory meas- 

 urement, and methods of detecting errors employed during this period 

 were essentially the same as tho.se formerly (1915) described. A new 

 serial closing apparatus has been added to the collecting equipment, 

 and attachments have been made to the Kofoid closing water bottle; 

 these additions are, therefore, briefly described. Furthermore, the 

 criteria used for rejecting doubtful hydrographic observations were 

 not treated fully enough in our former report (1915, pp. 21, 26) to 

 avoid the incorrect implication that certain observations may have 

 been omitted through oversight. Accordingly, these criteria are re- 

 discussed under the proper heading. 



