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 

 sta^e, we can find no more diminutive similitudes of the animal than those 



O t 



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. 



