72 REPRODUCTION AND LIFE HISTORY. 



never like a worm, or a fish, or a reptile. It is at most like 

 the embryonic stages of these, and it may also be noticed 

 that, as our knowledge is becoming more intimate, the 

 individual peculiarities of different embryos are becoming 

 more evident. But this need not lead us to deny the 

 general resemblance. 



Moreover, the individual life history is much shortened 

 compared with that of the race. Not merely does the one 

 take place in days, while the other has progressed through 

 ages, but stages are often skipped, and short cuts are dis- 

 covered. And again, many young animals, especially those 

 " larvae " which are very unlike their parents, often exhibit 

 characters which are secondary adaptations to modes of life 

 of which their ancestors had probably no experience. In 

 short, the individual's recapitulation of racial history is 

 general, but not precise. It is seen rather in the stages in 

 the development of organs (organogenesis) than in the 

 development of the organism as a whole. 



(4) Organic continuity between generations. Heredity. 

 Everyone knows that like tends to beget like, that off- 

 spring resemble their parents and their ancestors. Not 

 only are the general characteristics transmitted, but minute 

 features, idiosyncrasies, pathological conditions, inborn in 

 the parents, may be transmitted to the offspring. 



Many attempts have been made to explain this, but the 

 first suggestion with any scientific pretensions was that the 

 reproductive cells, which may become offspring, consist of 

 samples accumulated from the different parts of the body. 



This was a very old idea, but Herbert Spencer and 

 Charles Darwin gave it new life. According to Darwin's 

 " provisional hypothesis of pangenesis," the reproductive 

 cells accumulate gemmules liberated from all parts of the 

 body. In development these gemmules help to give rise to 

 parts like those from which they originated. This hypo- 

 thesis has been repeatedly modified, but except in the 

 general sense that the body may influence its reproductive 

 cells, " pangenesis " is discredited by most biologists. 



The idea which is now accepted with general favour is, 

 that the reproductive cells which give rise to the offspring 

 are more or less directly continuous with those which gave 

 rise to the parent. This idea, suggested by Owen, Haeckel, 



