GASTEROPODES. 319 
THE NAUTILINE. 
Among the most interesting facts pertaining to animal physiology, 
are the earliest form and condition of living beings. But, in attempting 
to discover what these may be, we are met by invincible obstacles, such 
as compel us to be content with assuming some later point of departure 
than the origin, and pursuing our course downwards. 
In ascending very high, we should probably find some invisible 
germ the source of future evolution ; and that, in all living beings, such 
evolution is attained through the medium of successive changes. Thus 
it has not appeared, that the earliest stage of mankind hitherto wit- 
nessed presents a human being in miniature, but that the subject then 
resembles a worm. 
Of later years naturalists have been ardently occupied with the 
study of metamorphoses, whereby many singular facts have been dis- 
closed. But as yet their history is less marked by continuity than by 
the aspect of objects at considerable intervals, a circumstance not to be 
wondered at, on duly appreciating the extraordinary difficulty of accom- 
panying or tracing the progress of living nature. 
We have just beheld a series, not a succession, of unintelligible facts 
in the history of the Doris, whereof no rational or satisfactory theory is 
offered in explanation. 
The figure of the parent is sufficiently obvious: it is reciprocally 
alike, wherever found in the adult state ; likewise there is the most per- 
fect resemblance, in form and habits, between the earlier young at large, 
and the specimens of amplest size, though the external parts be less 
numerous. But here we are arrested. On rising towards the embryonic 
stage, we can find no more diminutive similitudes of the animal than those 
which we have taken for comparison with the adult. 
It is reasonable to conclude, that the roe or spawn, so readily ob- 
tained in confinement, contains the elements of the offspring. Yet amidst 
thousands and tens of thousands of opportunities presented, we cannot 
trace any immediate connection between the living animal developed 
from it and the Doris itself. 
