ro THE BIOLOGY OF THE SEASONS 



the proper season though they are living in conditions 

 of great comfort. In such cases the internal periodicity 

 seems to assert itself even in the absence of the normal 

 stimulus. 



CURVES OF LIFE 



It is useful, then, to think of the course of life as an 

 ascending and descending curve sometimes like a semi- 

 circle, sometimes like an ellipse halved lengthwise, some- 

 times like a parabola, when seen from a distance. If we 

 get near it and peer closely into it, we find that the curve 

 has endless minor irregularities, like a pulse tracing or 

 like a barometer tracing. On the whole, however, there is 

 an up-grade, steep or gradual, from egg to embryo, from 

 embryo to larva, from larva to a miniature of the adult, 

 from this to the adolescent, and thence to the fully developed 

 organism ; then there is a crest, long or short, of maturity ; 

 and then there is a down-grade, marked by decreasing 

 vigour, sinking down through senescence to the nadir of 

 death. 



We rather like to think of the complete life as a parabolic 

 curve without beginning of days or end of years for who, 

 in face of the facts regarding ancestral inheritance and the 

 continuity of the germ-plasm, can insist very dogmatically 

 on beginnings or endings? What we call the individual 

 is part of a larger life. It is like a particular form of wave 

 in the sea, individualised for a brief moment, but only 

 intelligible as part of a great system of currents. 



Let us keep, however, to the broad facts. The creature 

 rises from the vita minima of early embryonic life to the 

 vigour of adolescence and to the full strength of maturity. 

 At its limit of growth it often reproduces, and this is, as 

 often, the beginning of a descent. Quickly or slowly, but 



