GENERAL FEATURES OF GROWTH 



519 



FIG. 2. 



ing properties : (a) It starts from O, since all organs must have a beginning. 

 (b) It ends at some point, T, when the animal dies, (c) The ordinates, 

 RL, PM, QN, SV, etc., tend generally 

 to increase. There is nothing im- 

 possible in a decrease such as PQ 

 (Fig. 2), much less in a stationary 

 period such as PR in Fig. 2 ; but the 

 general rule in Nature is growth, and 

 for the present the exceptions may be 

 left out of consideration. 



7. Resemblance to parents. Now 

 let the path for a certain organ in a 

 parent be OQP, PD being the size at 

 a time OD selected for observation or 

 measurement. At a corresponding time 

 in the life of one of the offspring let 

 the corresponding organ be observed or 

 measured, and found to be pD. Then 

 we know from experience that chil- 

 dren resemble their parents (I.), 

 and hence that pD will not be very 

 different from PD on the average. But 

 also we know that children are not 

 exactly like their parents, and may 

 differ from them either way (II.), 



FIG. 3. 



and hence pD will usually differ from PD ; and the difference may be in 

 either direction. 



8. But the two elementary principles just stated tell us more than 

 this. The resemblance and the difference are not applicable to a single 

 moment only such as OD ; they extend throughout life, and consequently 

 if we observe the corresponding organs at any previous time Od, we shall 

 find that dq is not very different from dQ, though, as a rule, not exactly 

 equal to it. 



It is easily seen that the path Oqp for the child will thus lie near to 



that OQP for the parent throughout 

 its whole length ; or in other words 

 the development of the child is a 

 recapitulation of the parental develop- 

 mentCHI.). 



9. The tendency to diverge. Let 

 us now suppose that the path OA is 

 followed by a certain individual. (For 

 convenience it and other paths are 

 drawn straight, but this in no way 

 affects the argument at present.) His 

 children may, and generally will, 

 follow paths near this, such as OB and Ob, which may differ from 

 OA in opposite directions. The children of OB will similarly, in 



X 



FIG. 4. 



