AN ESSA V ON LONGEVITY. 83 



much longer lived than the Naids and Chsetogaster/ 

 with few segments and one year of life. So, too, 

 the Echinoderms are tertiary aggregates, and con- 

 sequently have long life as compared with simple 

 Vermes. Tertiary aggregation acts in aiding lon- 

 gevity like the construction in five compartments of 

 the Great Eastern steam-ship, if one is injured and 

 lost, the others can go on without it, or even one 

 may survive by itself. The question of tertiary 

 aggregation brings us very near again to the dis- 

 cussion of individuality, which is not within our 

 scope. Remembering what was said at the outset 

 as to this, it is clear that tertiary aggregation acts 

 by merging many individualities into one, and thus 

 improving the chance of continued life. 



Social organization is a sort of tertiary aggregation, 

 in that newly-produced individuals do not separate 

 from but remain attached to the preceding generation, 

 supporting and ministering to the life of the older 

 constituents. Thus it is with civilized man. He is 

 supported in old age by the younger generations ; 

 the hope of, and confidence in, such support which 

 the younger individuals have, being the strongest 

 bond of society. 



' Naids and Chaetogaster are continually giving rise to new segments, 

 which separate and become new individuals. How long the life of one 

 original ancestor may be thus carried on by means of division is not 

 known ; but it is probably not for the immense period supposed by 

 some writers; for, when sexual organs develope, the worm ceases to 

 bud, and dies. 



G2 



