76 Scientific Proceedings, Royal Dublin Society. 



of individuals more directly than any other quality. It is, indeed, 

 self-favourable. The contest will therefore wax fiercer in an 

 accelerated degree till some give up. In this struggle it is hard 

 to see how a "tendency" to death after reproduction can be 

 encouraged by natural selection, for the individuals who have it 

 and those that have not got it reproduce alike, unless it can be 

 shown that such a tendency would involve increased reproductive- 

 ness or earlier reproductiveness. On the contrary it appears as if 

 those not having the tendency will rather produce the more abun- 

 dantly, and, by hypothesis, their descent is hereditarily uninfluenced 

 by increasing conditions of want. Again, if no external influences 

 affect the germ we have to suppose tendencies corresponding to 

 every periodic effect in nature. Thus it is very evident that the 

 phenomenon of sleep is based on external events. It is very 

 certain that what is now a physiological necessity originated in the 

 periodic restraint brought by the cold and darkness of night 

 acting upon the plastic organism since its initiation upon the 

 earth. 



In many cases, too, we can with great probability trace the time- 

 limit of the organism to definite periodic causes. This is the case 

 with death from climatological causes. Thus, among plants, annuals 

 possess but a year's life, and this limited length of life often per- 

 sists under artificial conditions. Again, these effects of old restraints 

 sometimes disappear under new climatic conditions. It is probable 

 that the time required to throw off the effects of an old restraint 

 will depend on how far it has become physiologically rooted in the 

 organism. Tendencies favourable to the new conditions will accele- 

 rate the changes which in some cases, possibly, would be very slow 

 in coming about without such help. In short, it is probable the 

 truth lies between the extremes of ascribing all to internal tenden- 

 cies and all to external causes. We know the organism is not a 

 stable configuration, as is the crystal, but one capable of extraordi- 

 nary adaptation. Every part of it possesses its vitality somewhat 

 on the conditions on whicli the top possesses its stability when in 

 motion, i.e. by the continual inflow of energy. Viewing the 

 organism simply as such a configuration of matter and energy, the 

 assumption that any part of it, growing along with and at the 

 expense of the rest, can remain isolated from the long- continued 

 action of external forces is certainly startling. 



