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Oct 18 1857. Suppose that those slight modifications (never mind at what period caused) by which they make final great difference) first appeared according to some such law, that 1/100,00 first appeared in fully mature animals & 1/100,000 cd just be detected at some very early period of embryonic life all the vast remainder gradually increasing in number from these two extremes & preserved in some intermediate periods, Then & after 100,000 changes the embryo before supposed period wd not be at all only just affected - at subsequent periods very little affected, but at same period young growing animal considerably affected, & mature animal alone receiving full complement of change. But often ten times 100,000 changes, to embryo at same very early period

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would have been slightly affected at this very early period. Whence it follows, that if comparing Dog & Pig, there has been a greater number of modification from the common analogous form of common species, whence they started, than there has been Pig & Sheep, then the embryos of these latter will have been modified at less early period. I do not suppose that the law is as I have put it - the modification of some part very likely effects embryo more than others. On this scheme we need not consider period of branching off, which will I believe go with time, as selection & extinction must take time.

v. von Baer in Scientific memoirs - The above explains period of Branching off of fish & Mammals &c. But can it be applied to organs in same animal. Brulle says so - Huxley has [covered] no false. Terms may be in later part of change.