82 Scientijic Proceedings, Royal Duhlin Society. 



If we lay out waves as above to a common scale of time for 

 different species, the difference of longevity is shown in the greater 

 or less number of vibrations executed in a given time, i. e. in greater 

 or less "frequency." We cannot indeed draw the curvature 

 correctly, for this would necessitate a knowledge which we have 

 not of the activity of the organism at different periods of its life- 

 history, and so neither can we plot the direction of the organic 

 line of propagation with respect to the axes of reference as this 

 involves a knowledge of the mean activity. However much of 

 this we may know in the future, at present if I mistake not, such 

 data are not available. 



Much might be tery easily done in this direction by compara- 

 tive estimates of the demand at various periods of life. Thus, 

 by supplying an individual with the same sort of food throughout 

 its life, and assuming unit weight of this food as unit of energy 

 on the diagram, the curvature is approximately determinable. In 

 this way the differences in the time-energy function of male and 

 female at the various stages of life-history might be found. 

 Observations on the latter during pregnancy would enable the 

 curve to be traced back to the foetal period of life. 



The group of curves which follow (fig. 5} are entirely imaginary, 

 except in respect to the approximate longevity of the organisms. 

 Man as the most complex and many-sided animal is drawn as if 

 his activity was the greatest, the Dog is put above the Tortoise, 

 for this last is a sluggish creature, except in the heat of summer, 

 and even then its diet and its exertions are limited. 



It is probable, as before observed, that to conditions of struc- 

 tural development, the question of longer or shorter life is in 

 a great degree referable. Thus, development along lines of large 

 growth will tend to a slow rate of reproduction from the simple 

 fact that unlimited energy to supply a large number of costly 

 reproductive acts is not procurable, whatever we may assume as 

 to the strength or cunning exerted by the individual in its efforts 

 to obtain its supplies. On the other hand, development along 

 lines of small growth, in that reproduction is less costly, will 

 probably lead to increased rate of reproduction. It is, in fact, 

 matter of general observation that in the case of larger animals 

 the rate of reproduction is most generally slower than in the case 

 of smaller animals, and, as we have seen, it appears that the rate 



