46o LIFE : OUTLINES OF GENERAL BIOLOGY 



There are, he supposes, two lock-gates in a stream, which are kept 

 in position by powerful springs. The water accumulates above the 

 gates, until there is so great a pressure that the resistance of the 

 springs is overcome and the gates are driven open. After the rush of 

 water has gone through, the springs will come into effective action, 

 and close the gates, until the same sequence has to be repeated. 

 Anabolism corresponds to the accumulation of the head of water; 

 katabolism is the bursting open of the gates and the down-rush; 

 the springs of the gates have their analogues in the colloidal proper- 

 ties of protoplasm. We do not suppose that Sager has solved the 

 problem of the alternating preponderances of anabolism and kata- 

 bolism, but his thoughtful contribution is very welcome. It is 

 something to have seen that there is a problem at all. 



In any case, all agree that the chemical routine of living creatures 

 often shows a rhythmic periodicity of winding-up and running- 

 down ; that is to say, these alternative processes often show a regular, 

 methodical repetition of varying and even contrasted intensities. 

 Such autonomic rhythms are characteristic of living creatures, and 

 are fundamental to the further and secondary rhythms, which are 

 associated with periodic environmental changes — e.g. diurnal, tidal, 

 or seasonal. 



ADAPTATIONS IN REPRODUCTION.— In typical Vertebrate 

 animals, and in many Invertebrates, a rhythm has been established 

 in the body such that reproductive activity sets in at the time of 

 year favourable to the starting of a new generation or a new family. 

 This is, of course, a very complex adjustment ; for while it is of great 

 importance that the young should be bom at a favourable time of 

 year, this may be secured not only by a change in the pairing time, 

 but als(j by a change in the duration of antenatal life. Similarly 

 among seed-plants there may be a long or a short interval between 

 the time of pollination and the time of seed-scattering. A seed, too, 

 may remain for a long time quiescent, before it becomes a seedling. 

 The life-histories that are most readily interpreted are those of 

 annual animals and annual i)lants in countries with well-defined 

 seasons, for summer is then the time of pairing and pollinating, 

 autumn the time of early development and separation from the 

 moribund parent, winter the time of lying latent and well-protected, 

 whether as seed or cocoon, and spring the time of resumed develop- 

 ment and youth. But the variations on this theme are wellnigh 

 bewildering. Rats, mice, rabbits, etc., have three or four litters in 

 the year, but this is very different from the state of affairs in not a 

 few short-lived insects which have several generations in a summer. 

 There are slowly developing types, like elephants, "century plants", 

 etc., that are not mature till many years have passed; there are some 

 midges and worms and two or three amphibians that arc repro- 



