44 EMBRYOLOGY 



object gained in varying form &c. of foetus (beyond 

 certain adaptations to mother's womb) and there- 

 fore selection will not further act on it, than in 

 giving to its changing tissues a tendency to certain 

 parts afterwards to assume certain forms. 



Thus there is no power to change the course of 



reproduction, shape of horns, case of old brothers dying of same disease]. 

 And we know that the germinal vesicle must have been affected, though no 

 effect is apparent or can be apparent till years afterwards, no more 

 apparent than when these peculiarities appear by the exposure of the full- 

 grown individual. (That is, " the young individual is as apparently free from 

 the hereditary changes which will appear later, as the young is actually free 

 from the changes produced by exposure to certain conditions in adult life.") 

 So that when we see a variety in cattle, even if the variety be due to act of 

 reproduction, we cannot feel sure at what period this change became 

 apparent. It may have been effected during early age of free life (or) fetal 

 existence, as monsters show. From arguments before used, and crossing, 

 we may generally suspect in germ ; but I repeat it does not follow, that the 

 change should be apparent till life fully developed ; any more than fatness 

 depending on heredity should be apparent during early childhood, still 

 less during fetal existence. In case of horns of cattle, which when inherited 

 must depend on germinal vesicle, obviously no effect till cattle full-grown. 

 Practically it would appear that the [hereditary] peculiarities characterising 

 our domestic races, therefore resulting from vesicle, do not appear with 

 their full characters in very early states ; thus though two breeds of cows 

 have calves different, they are not so different, grey-hound and bull-dog. 

 And this is what is (to) be expected, for man is indifferent to characters of 

 young animals and hence would select those full-grown animals which 

 possessed the desirable characteristics. So that from mere chance we 

 might expect that some of the characters would be such only as became 

 fully apparent in mature life. Furthermore we may suspect it to be a law, 

 that at whatever time a new character appears, whether from vesicle, or 

 effects of external conditions, it would appear at corresponding time 

 (see Origin, Ed. i. p. 444). Thus diseases appearing in old age produce 

 children with d., early maturity, longevity, old men, brothers, of 

 same disease young children of d. I said men do not select for 

 quality of young, calf with big bullocks. Silk-worms, peculiarities which, 

 appear in caterpillar state or cocoon state, are transmitted to corre- 

 sponding states. The effect of this would be that if some peculiarity was 

 bora in a young animal, but never exercised, it might be inherited in young 

 animal ; but if exercised that part of structure would be increased and 

 would be inherited in corresponding time of life after such training. 



I have said that man selects in full-life, so would it be in Nature. In 

 struggle of existence, it matters nothing to a feline animal, whether kitten 

 eminently feline, as long as it sucks. Therefore natural selection would act 

 equally well on character which was fully (developed) only in full age. 

 Selection could tend to alter no character in foetus, (except relation to 

 mother) it would alter less in young state (putting on one side larva condition) 

 but alter every part in full-grown condition. Look to a fetus and its parent, 

 and again after ages fetus and its (i.e. the above mentioned parents) 

 descendant ; the parent more variable (?) than fetus, which explains all. 



