1094 LIFE : OUTLINES OF GENERAL BIOLOGY 



parents and ancestors, and often distinguishing one member of a 

 family from another. They may affect quantitative characters — a 

 little more of this and a Httle less of that, or they may be qualita- 

 tively novel, e.g. some new constitutional or biochemical feature; 

 they may be structural or functional; and they are often negative 

 as weU as plus. Some may be described as changes in the rate and 

 rhythm of metaboUsm ; others are lengthenings out or shortenings 

 down of arcs on the life-curve, e.g. an extension of youth or a 

 shortening of mature activity. A new departure may be progressively 

 accentuated from generation to generation, and persistence on one 

 Une for a succession of generations is said to illustrate orthogenic 

 change. When a novelty arises abruptly without intergrades con- 

 necting it with less marked but similar features in the parents or 

 ancestry, it is called a mutation, and may be large or smaU in amount ; 

 it turns out to be independently heritable, without blending or 

 breaking up, and illustrates Mendelian inheritance. Other varia- 

 tions, less clear-cut, intergrading in amount, are often called fluctua- 

 tions. They do not "mendeUse". 



4. New departures that continue hereditarily from generation 

 to generation, and may be increased by selection, are usually 

 regarded as due to changes in the constitution of the egg-cells and 

 sperm-ceUs, or as the outcome of the fertiUsation of the egg-cell by 

 the sperm-cell. They are briefly spoken of as germinal variations, 

 and the modem idea, which Darwin did not clearly realise, is that 

 the changes which crop up in the developing body are the expressions 

 of antecedent germinal permutations and combinations, gains and 

 losses, disturbances or enhancements. It is because of their germinal 

 origin that true variations tend to be continued on to the next 

 generation, just like the weU-established inheritance in general. 

 This begetting of like by like depends on the fact known as the 

 continuity of the germ-plasm, an idea particularly associated with 

 Weismann. The general idea, then, is that the fluctuations and 

 mutations that form the raw material of further evolution have a 

 germinal origin. 



5. But in the present book the thesis is also stated that the organ- 

 ism is not restricted in its varying to the time when it is implicit in 

 the one-cell phase of its being, but may vary constitutionally later 

 on, e.g. by becoming more nutritive or more reproductive, by 

 becoming more foUar or more floral, by shortening or elongating the 

 axis in flowering plants, by emphasising anabolism or katabolism, 

 and so forth. Yet to the more Weismannian author it appears that 

 these apparently somatic variations are au fond germinal variations 

 which express themselves within certain old-established Umits or 

 trends of development and metabolism. The expHcit organism varies 

 along prescribed constitutional lines, but the impulse and bias of 

 the varying is germinal. 



