492 LIFE HISTORY STUDIES OF ANIMALS. 



reproach to zoologists. The partially-kiiown migration of the eel could 

 not be harmonized with the ordinary rule of migratory fishes. We 

 tried to explain the passage of marine fishes into rivers at spawning 

 time by the supposition (a true supposition, as I think) that the river is 

 less crowded than the shallow seas, and therefore a region in which 

 competition is less severe. The river is to some migratory fishes what 

 the tundras of Siberia are to some migratory birds, places compara- 

 tively free from dangerous enemies, and therefore fit for the rearing of 

 the helpless young. But the eel broke the rule and cast doubt upon 

 the explanation. The salmon, sturgeon, and lamprey feed and grow in 

 the sea and enter rivers to spawn. The eel feeds and grows in rivers 

 but enters the sea to spawn. What possible explanation could meet 

 cases thus diametrically opposite? 



This was the state of matters when Grassi undertook to tell us that 

 part of the history of the eel which is transacted in the sea. When it 

 leaves the river it makes its way to very deep water and there under- 

 goes a change. The eyes enlarge and become circular instead of ellip- 

 tical; the pectoral fins and the border of the gill cover turn black; the 

 reproductive organs, only to be discovered by microscopic search before 

 this time, enlarge. The eels, thus altered in appearance and structure, 

 lay their eggs in water of not less than 250 fathoms depth. The upper 

 limit of the spawning ground is nearly three times as far from sea level 

 as the 100 fathom line, which we arbitrarily quote as the point at which 

 the deep sea begins. The eggs, which are large for a fish (2.7 millime- 

 ters diameter), float, but do not rise. The young which issue from them 

 are quite unlike the eels of our rivers; they are tapelike, transparent, 

 colorless, devoid of red blood, and armed with peculiar teeth. A num- 

 ber of different kinds of such fishes had been previously known to the 

 naturalist as Leptocei)hali. Grlinther had conjectured that they were 

 abnormal larvae, incapable of further development. Grassi has, how- 

 ever, succeeded in proving that one of these Leptocephali {L. hreviros- 

 tris) is simply a larval eel ; others are larvae of congers and various 

 muraenoid fishes. He has with infinite pains compared a number of 

 Leptocephali, and coordinated their stages, making out some particu- 

 larly important ones by the direct observation of live specimens. 



You will not unnaturally ask how Grassi or anybody else can tell 

 what goes on in the sea at a depth of over 250 fathoms. His inquiries 

 were carried on at Messina, where the local circumstances are very 

 fortunate. Strong currents now and then boil up in the narrow strait, 

 sweeping to the surface eggs, larvae, and a multitude of other objects, 

 which at ordinary seasons lie undisturbed in the tranquil depths. Fur- 

 ther information has been got by dredging, and also by opening the 

 body of a sunfish {Orthagoriscus mola), which at certain times of the 

 year is taken at the surface and is always found to contain a number 

 of Leptocephali. When a Leptoceplialus has completed its first stage 

 of growth it ceases to feed, loses bulk, and develops pigment on the 

 surface of the body. At the same time the larval teeth are cast and 



