THE CYCLE OF LIFE 469 



But let us return to the fertilized eggs. They develop 

 quickly and hatch in about a fortnight. About a month 

 later, when about half an inch long, the larvae leave the 

 nest and seek out quiet stretches of the river. They diSer 

 from the adults in the horseshoe shape of the Ups, in having 

 a sieve of barbels guarding the true mouth, in the details 

 of their respiratory system, in having much less developed 

 unpaired fins, and in being bhnd. They form burrows 

 in the sand or mud, and feed on small aquatic animals. 

 It is very difficult for ordinary eyes to see any difference 

 between the larvse of the various species, and the technical 

 name Ammoccetes hranchialis is applied to them all. 



After three or four years of a somewhat monotonous 

 juvenile hfe, the larvse begin to grow up. They put 

 away their larval characters and pass through a metamor- 

 phosis, just as a tadpole does in turning into a frog. This 

 is accomphshed in the autumn months between the end of 

 August and mid-October. The horseshoe Ups are changed 

 into a circle, the barbels into papillae, the suctorial disc is 

 formed, the teeth develop, internal adjustments are effected, 

 the creatures become more active, and pass down the rivers 

 to the sea or the great lake, where they become strictly 

 fish-eaters. After two or three years of vigorous hfe and 

 rapid growth the young lampreys have quite grown up, 

 and they return up the streams to their old cradle-area, 

 which is also the place of their death- 



A Strasburg fisherman called Baldner is said to have 

 convinced himself more than two hundred years ago that 

 ' niners ' grew into lampreys, but his correct conclusion 

 was not accepted till 1826, when A. Miiller observed the 

 whole life-history of the brook lamprey — ^the eggs develop- 

 ing into niners, and these changing into the adult forms. 



