144 SECRETS OF ANIMAL LIFE 



a prolonged larval period has been interpolated. 

 Out of the egg-shell of a cockroach there comes 

 a miniature of the adult, but out of a butterfly's 

 there emerges a minute caterpillar with very little 

 hint of its parentage. It feeds and grows and 

 molts its husk, and this logical sequence is repeated 

 over and over again. The caterpillar gains strength 

 and stores up nutritive reserves; it undergoes a 

 remarkable metamorphosis, most of the old larval 

 body breaking down and a fresh start in develop- 

 ment being made on a new architectural plan. 

 Eventually the winged butterfly emerges, as it were, 

 by a second birth, and enters upon a phase of life 

 which is preoccupied with reproduction and only 

 secondarily (if at all) concerned with nutrition. 

 The relatively long caterpillar period makes the 

 ecstasy of the butterfly possible. A very remarkable 

 achievement has resulted from the lengthening out 

 of the larval phase, and in many life-histories we 

 hear, so to speak, the same tune. The mayflies 

 or Ephemerides are often almost diagrammatic, for 

 many have two or three years of subaquatic larval 

 life and two or three days (or less) of aerial and 

 reproductive activity. In the sea-lamprey we find 

 a somewhat similar punctuation of life but it is 

 notably improved upon. For after a long larval 

 fluviatile period, sometimes of four years, there is a 

 phase of vigorous adolescence and adult life in the 

 sea. But the curve ends in the same way an 

 almost vertical drop after reproduction. In the 

 common eel there is a greatly elongated larval 



