160 THE CONTROL OF LIFE 



turely, losing all their elasticity. One of Professor 

 Child's very curious experiments with Planarian 

 worms shows that these creatures may he horn old if 

 their parents and grandparents are restricted to un- 

 suitable food. So, though we do not know precisely 

 how, some children are born old. Similarly it is said 

 of the victims of lead-poisoning that young men often 

 look middle-aged. 



On the other hand, there are many rejuvenescent 

 types in whom certain threads remain young even 

 when the tale of years is a very long one. Montaigne 

 wrote of his father : "I have seene him, when hee was 

 past threescore years of old, mocke at all our sports, 

 and out-countenance our youthfull pastimes, with a 

 heavy furr'd gowne about him leap into his saddle; 

 to make the pommada round about a table upon his 

 thumb ; and seldom to ascend any staires without 

 skipping three or foure steps at once." He at any 

 rate might have been appropriately called " old boy." 



Illustrations. — A few examples may be given of the 

 way in which life-histories differ — by altering the 

 * time ' of the different stretches of the hfe-curve, 

 elongating one part and compressing another, length- 

 ening here and telescoping there. Mayflies often have 

 two or three years of sub-aquatic juvenile life, and 

 only two or three days of adult aerial life. The lam- 

 preys are young for four or five years, and f ally formed 

 for some years, but they die abruptly after spawn- 

 ing, as eels seem also to do. The strange Peripatus 



