loo SCIENCE PROGRESS 



are larger, the snout is sharp, the Hps are thin and the pectoral 

 fins are black and pointed. Their flesh is very rich in fat, which 

 is no doubt expended in the development of the genital glands 

 and in their journey across the ocean. How long this journey 

 occupies is not known : possibly eels that leave Britain in the 

 autumn may cross the ocean in time to breed the following 

 spring, but it seems hardly likely that eels from Finland or 

 Egypt could cover the distance in less than a year. At their 

 breeding place the ocean is over 3,000 fathoms deep, but it is 

 improbable that they breed on the bottom or anywhere near it. 

 One thing that we may be sure of is that all the eels die after 

 spawning ; no fish which makes a breeding journey of from 2,000 

 to 4,000 miles can be expected to do so more than once in its 

 life, and we may infer from the analogy of the Sea-lamprey 

 and other fishes which breed only once that the formation of 

 the genital glands entails the degeneration of all the other 

 organs, rendering recovery after breeding impossible. 



It will be seen that this remarkable life-history may be 

 divided into four main stages : — 



1. The pelagic larval stage, a period of active growth and 

 passive migration. 



2. The transformation into the elver, or young eel. 



3. Growth of the eel, 



4. Change into the silver eel, and breeding migration, ending 

 in death after breeding, 



Schmidt's work has been characterised by extraordinary 

 persistence and insight, and it is certainly no mean contribution 

 to the advance of science to have made clear this unique life- 

 history. Moreover, the Zoarces investigation, undertaken as 

 a check on his conclusions from statistical data in Anguilla, 

 proved so full of interest that it has been continued and ex- 

 tended, and promises to be of the utmost importance in helping 

 to solve the problem of the origin of local races. Finally, in 

 the voyages made under Schmidt's leadership it was not only 

 larvae of Anguilla that were caught, but a host of pelagic organ- 

 isms of all kinds. These have been preserved for study, with 

 full data, and already several volumes have appeared, giving 

 some of the hydrographical and biological results of the voyages 

 of the Thor, and marking a large advance in knowledge of life 

 in the sea and the conditions that determine its distribution. 



