2(> LIFK : OUTLINES OF GENERAL BIOLOGY 



sion. some of fundamental imj>ortance and others relatively trivial; 

 the past lives on in the present; often the individual shows, in 

 van-ing degree, evidence that it is "climbing up its own genealogical 

 tree". Sometimes the embryo develops steadily and directly into 

 the likeness of its kind, as in birds and mammals, with only traces 

 of circuitousness, such as notochord and gill-clefts disclose — tell- 

 tale evidence of the lien the past continues to hold on the present. 

 In many other cases development is anything but direct, for 

 there is an inter|x)lation of larval stages, often in marked adaptation 

 to dithcult circumstances. Thus frogs and toads, the modern repre- 

 sentatives of an ep(X'h-making colonisation of the dry land in the 

 late Devonian jxTiod, have not freed themselves from the ancestral 

 nvtluvl of liberating the eggs in the water, a relatively much safer 

 cradle than terra tirma can afford. The prolonged tadpole stages 

 imply a continuance of the development in comparative safety, 

 and what leaves the water is a fully formed air-breathing miniature 

 of tin* adult frog. The caterpillar is a voraciously feeding and 

 rapidly growing larval form, accumulating stores of energy, which 

 are |)artly used in the re-building that follows down-breaking in 

 metamorpho>is, yet leave enough over to enable the butterfly to 

 lead its joyous life, with little in the way of nutritive exertion, up 

 to its fatal climax of reproduction. But in all cases, however diverse 

 in detail, development is the progressive attainment of full-grown 

 complexity from comparatively undifferentiated simplicity, and 

 there is no characteristic of the living organism more distinctive 

 than thi*;. 



BEHAVIOUR, REGISTRATION, AND EVOLUTION. -A third 

 triad of (jualities which are distinctive of the living organism may 

 l)c summed up in the words behaviour, registration, and evolution, 

 in which as in previous triads an underlying unity may perhaps be 

 discerned . 



Bkhavioir. Herbert Sjx'ncer spoke of life as "effective 

 res|>onsr". and from the amaba upwards we recognise among 

 animals the power of linking actions in a chain so that the result 

 is behaxiour always purposive and in the higher reaches purpose- 

 ful. Responses are common in the inorganic world— from gentle 

 weathering to volcanic explosion but non-living things do not 

 show thr living creature's power of reacting in a self-preservative 

 WAV. Amf>ng plants, for various reasons, such as the fixed habit 

 of the gnat majoritv and the enclosing of the cells in cellulose, 

 there is relativdv little exhibition of that purposive "doing of 

 things" whirh wr call behaviour, but we must not forget the 

 insurgent activities of climbing plants or the carnivorous adventures 

 of Wnus's Mv-trap and the Sundew. An entire section of this book is 

 flevoted to illustrating the long inclined plane of behaviour. 



