182 Darwin and Embryology 
least as long as it is at the present time. The qualification implied 
by the words in italics is necessary, for it is clearly possible that the 
external conditions then existing were not suitable for the production 
of all the stages of the potential life-history, and that what we call 
organic evolution has consisted in a gradual evolution of new en- 
vironments to which the organism’s innate capacity of change has 
‘enabled it to adapt itself. We have warrant for this possibility in 
the case of the Axolotl and in other similar cases of neoteny. And 
these cases further bring home to us the fact, to which I have already 
referred, that the full development of the functional reproductive 
organs is nearly always associated with the final stages of the life- 
history. 
On this view of the succession of characters in the life-history of 
organisms, how shall we explain the undoubted fact that the develop- 
ment of buds hardly ever presents any phenomena corresponding to 
the embryonic and larval changes? The reason is clearly this, that 
budding usually occurs after the embryonic stage is past; when the 
characters of embryonic life have been worked out by the machine. 
When it takes place at an early stage in embryonic life, as it does in 
cases of so-called embryonic fission, the product shows, either partly 
or entirely, phenomena similar to those of embryonic development. 
The only case known to me in which budding by the adult is 
accompanied by morphological features similar to those displayed 
by embryos is furnished by the budding of the medusiform spore-sacs 
of hydrozoon polyps. But this case is exceptional, for here we have 
to do with an attempt, which fails, to form a free-swimming organism, 
the medusa; and the vestiges which appear in the buds are the 
umbrella-cavity, marginal tentacles, circular canal, etc., of the medusa 
arrested in development. 
But the question still remains, are there no cases in which, as 
implied by the recapitulation theory, variations in any organ are 
confined to the period in which the organ is functional and do not 
affect it in the embryonic stages? The teeth of the whalebone whales 
may be cited as a case in which this is said to occur; but here the 
teeth are only imperfectly developed in the embryo and are soon 
absorbed. They have been affected by the change which has, 
produced their disappearance in the adult, but not to complete 
extinction. Nor are they now likely to be extinguished, for having 
become exclusively embryonic they are largely protected from the 
action of natural selection. This consideration brings up a most 
important aspect of the question, so far as disappearing organs are 
concerned. Every organ is laid down at a certain period in the 
embryo and undergoes a certain course of growth until it obtains 
full functional development. When for any cause reduction begins, 
