Sbptembee 3, 1920] 



SCIENCE 



215 



if all the land were washed down into the sea 

 the whole globe would be covered by an ocean 

 averaging about two miles in depth. "We know 

 the distribution of temperatures and salinities 

 over a great part of the surface and a good 

 deal of the botton of the oceans, and some of 

 the more important oceanic currents have 

 been charted and their periodic variations, 

 such as those of the Gulf Stream, are being 

 studied. We know a good deal about the or- 

 ganisms floating or swimming in the surface 

 waters (the epi-plankton), and also those 

 brought up by our dredges and trawls from the 

 bottom in many parts of the world — although 

 every expedition still makes large additions to 

 knowledge. The r^ion that is least known to 

 us, both in its physical conditions and also its 

 inhabitants, is the vast zone of intermediate 

 waters lying between the upper few hundred 

 fathoms and the bottom. That is the region 

 that Alexander Agassiz from his observations 

 with closing tow-nets on the Blake Expedition 

 supposed to be destitute of life, or at least, as 

 modified by his later observations on the 

 Albatross, to be relatively destitute compared 

 with the surface and the bottom, in opposition 

 to the contention of Murray and other oeeano- 

 graphers that an abundant meso-plankton was 

 present, and that certain groups of animals, 

 such as the Challengerida and some kinds of 

 Medusae, were characteristic of these deeper 

 zones. I believe that, as sometimes happens in 

 scientific controversies, both sides were right 

 up to a point, and both could support their 

 views upon observations from particular re- 

 gions of the ocean under certain circumstances. 

 ! But much still remains unknown or only 

 imperfectly known even in matters that have 

 long been studied and where practical appli- 

 cations of great value are obtained — such as 

 the investigation and prediction of tidal phe- 

 nomena. We are now told that theories re- 

 quire re-investigation and that published 

 tables are not sufficiently accurate. To take 

 another practical application of oceanographic 

 work, the ultimate causes of variations in the 

 abimdance, in the sizes, in the movements 

 and in the qualities of the fishes of our coastal 

 industries are still to seek, and not withstand- 



ing volumes of investigation and a still 

 greater volimie of discussion, no man who 

 knows anything of the matter is satisfied with 

 our present knowledge of even the best-known 

 and economically most important of our fishes 

 such as the herring, the cod, the plaice and 

 the salmon. 



Take the case of our common fresh-water 

 eel as an example of how little we know and 

 at the same time of how much has been dis- 

 covered. All the eels of our streams and lakes 

 of ]Sr.-W. Europe live and feed and grow 

 under our eyes without reproducing their 

 kind — no spawning eel has ever been seen. 

 After living for years in immaturity, at last 

 near the end of their lives the large male and 

 female yellow eels undergo a change in ap- 

 pearance and in nature. They acquire a 

 silvery color and their eyes enlarge, and in 

 this bridal attire they commence the long 

 journey which ends in maturity, reproduction 

 and death. From all the fresh waters they 

 migrate in the autumn to the coast, from the 

 inshore seas to the open ocean and still west- 

 ward and south to the mid-Atlantic and we 

 know not how much further — for the exact 

 locality and manner of spawning has still to 

 be discovered. The youngest known stages of 

 the Leptoeephalus, the larval stage of eels, 

 have been found by the Dane, Dr. Johannes 

 Schmidt, to the west of the Azores where the 

 water is over 2,000 fathoms in depth. These 

 were about one third of an inch in length and 

 were probably not long hatched. I can not 

 now refer to all the able investigators — Grassi, 

 Hjort and others — ^who have discovered and 

 traced the stages of growth of the Lepto- 

 eephalus and its metamorphosis into the 

 " elvers " or young eels which are carried by 

 the North Atlantic drift back to the coasts of 

 Europe and ascend our rivers in spring in 

 countless mjrriads but no man has been more 

 indefatigable and successful in the quest than 

 Dr. Schmidt, who in the various expeditions 

 of the Danish Investigation Steamer Thor 

 from 1904 onwards found successively younger 

 and younger stages, and who is during the 

 present simamer engaged in a traverse of the 

 Atlantic to the West Indies in the hope of 



