34 AGE, GROWTH, AND DEATH 



appearing of an advance in organisation, of correlated 

 loss of parts, and when we get far enough down the 

 scale, senescence becomes very vague. The change 

 from youth to old age in a coral or in a sponge is at 

 best an indefinite matter. 



I should like, did the length of the course permit, 

 to enlarge greatly upon this aspect of the question, 

 and explain to you how it is that as the organism 

 rises higher and higher in the scale, old age becomes 

 more and more marked, and in no animal is old age 

 perhaps so marked, certainly in no animal is it more 

 marked, than in ourselves. The human species 

 stands at the top of the scale and it also suffers most 

 from old age. We shall learn, I hope, more clearly 

 later on in the course of these lectures, that this fact 

 has a deeper significance, that the connection be- 

 tween old age and advance in organisation, advance 

 in anatomical structure, is indeed very close, and that 

 they are related to one another somewhat in fashion 

 of cause and effect ; just how far each is a cause and 

 how far each is an effect it would perhaps be prema- 

 ture to state very positively ; but I shall show you, I 

 think in a convincing way, that the development of 

 the anatomical quality, or in other words of what we 

 call organic structure, is the fundamental thing in the 

 investigation of the processes of life in relation to 

 age. We can see it illustrated again very clearly 

 indeed when we turn to the study of plant life, for 

 plants also grow old. Take a leaf in the spring. 

 It is soft as the bud opens. The young leaf is deli- 



