Sottas—On the Origin of Freshwater Faunas. 115 
numerous to make this result of a free larval existence clearly appear, so that the 
not very highly endowed animal may enjoy the adult state for a very considerable 
period. ‘To rightly estimate the value of this hypothesis, we ought to know at 
least approximately the limits of age of various animals in the adult state, and the 
length of time they respectively pass in the larval state, as well as the changes 
which they pass through; and these data are almost wholly wanting, and not 
unnaturally, since no intelligent man, unprompted by some suggestions such as 
here made, would care to set about the laborious investigation which their 
ascertainment would involve, merely for the sake of tabular results. Something, 
however, may be learnt from various of the higher animals. Thus we may poimt 
to the Ephemeride, which, after a prolonged larval existence, die soon after 
attaining maturity. So, too, the butterflies and moths, which do not live long 
after oviposition. A still more important consequence, however, would seem to 
follow from the premature ageing due to a free larval existence; and that is the 
comparatively early exhaustion of the power of undergoing transformational 
change ; the adult or comparatively stable state is reached sooner than it other- 
wise would be, and the chances of further development are correspondingly di- 
minished. 
If we pass to the consideration of the opposite case, we find that the embryo 
within the egg is in a much superior position to the free larva. In most cases, all 
that it has to do, besides undergoing transformational changes, is to feed upon 
nourishment already prepared for it, needing scarcely any preliminary digestion, 
but capable of immediate absorption by the cells of the embryo. When the 
embryo is hatched, it enters upon the world with its cells scarcely used; their 
capacity for work has comparatively had small demands made upon it, and thus a 
longer life awaits them in the mature state, when the faculties of the organism 
are most highly endowed. 
Thus, in contrast with the Ephemeride, we may cite the ants and bees, which, 
while in the larval stage, are carefully nourished at the expense of the com- 
munity, and some of which, after leading the life of grubs, enjoy an interesting and 
protracted existence. Further, the cells of a young animal just born would 
appear to be in a particularly plastic state, so that they are peculiarly ready 
to respond to the action of the environment. Many changes might be induced in 
the young animal at this critical period, the effects of which would be afterwards 
manifested as variations in its offspring. 
Again, the longer life in the mature state, acquired by those forms which are 
saved from the drudgery of a larval existence, offers increased opportunities for 
evolution to the adult animals, so that a progressive development starting from 
higher and higher platforms is directly favoured. 
But not only is a longer existence assured to the adult—existence in the 
embryonic state is shortened, and perhaps here the influence of seclusion is most 
