8 INTRODUCTION. 



Thus, it is probable, that a previous diffusion of elementary germs 

 promotes the successive regenerations ; that their development ensues 

 in perfecting the new portion, rather than in the depositation of new 

 matter from the old, to be modified into form. 



The history of the Poh^jius, and the reproductions of the Actinia, to- 

 gether with those of some of the limacine tribes, have been long familiar. 

 Several, perhaps most of the purely vermicular race, may be cut in 

 twenty portions with impunity, and many subdivide spontaneously, 

 while each becomes perfect by acquiring the defective organization. 

 These facts are an impediment to ascertaining the real dimensions of the 

 parent subjects. They render them questionable. 



Regeneration do v\ai wards is obviously more readily effected than 

 the restoration of defective parts upwards. New development speedily 

 follows mutilation towards the lower extremity. 



In the violent or spontaneous di^'ision of animals, wherein repro- 

 duction is most vigorous, it ensues both downwards from the principal 

 portion of the original, if unequally made, and it generates from the 

 sundered portion upwards. 



The generation of cotemporary supernumerary parts may be ob- 

 tained by sundering a fragment from the posterior extremity of the 

 Amphitrite vcntilah'um. A beautiful and complex branchial plume is 

 generated upwards, while the original branchial plume continues in full 

 vigour. Both fulfil their specific purposes. If it cannot be affirmed 

 that a germ is newly formed b}^ new depositation of elementary matter, it 

 may be conjectured that aU the rudiments of the regenerated portion 

 pre-existed separation of the original animal's body. 



All animated beings seem to undergo a certain metamorphosis be- 

 tween the date of then- early origin, and their attainment of perfection. 

 Some are passing through it whUe still connected with the parent ; in 

 others the changes advance long afterwards. 



It is not obvious whether any kind of metamorphosis enters the 

 simple development of animals as they enlarge in natural growth, or 

 in the regeneration of theii' defective parts. While in progressive ad- 

 vances to perfection, metamorphosis, as present to the eye, consists in 



