2 PREFACE TO THE 



precedence of one or more generations, whose function it 

 is, as it were, to prepare the way for the later, succeeding 

 generation of animals destined to attain a higher degree 

 of perfection, and which are developed into the form of 

 the mother and propagate the species by means of ova, 

 can, I believe, be demonstrated in not a few instances in 

 the animal kingdom. 



The first division of the lower animals, in which I have 

 observed its existence, are the Medusce (Chap. I) as they 

 have been exhibited to us in the observations of Sars 

 and Siebold, and especially of the former. 



The polypiform animal Sc7/^histoma-Strobila, into which 

 the offspring from the ova of all the Medusae is meta- 

 morphosed, and which, though it does not itself become a 

 perfect Medusa, produces the larvcB which do, is in my 

 opinion a precedent generation of the kind in question ; 

 and according to my own researches it resembles a polype 

 only externally, and is in its structure really a Medusa, 

 though one which is attached by means of a stem to fixed ob- 

 jects. So also in the claviform Folypes, Corynce (Chap. II), 

 the so-termed polypeliead is a precedent individual 

 which produces the more perfect and differently formed 

 medusa-like campanulate animals which are developed in 

 succession at the base of the clavate head, and the develop- 

 ment of which, varies very much in the different species, 

 before their separation from the preparative individual, 

 and their becoming competent to propagate the species 

 by ova, from which again proceed the Corynse or prepa- 

 rative individuals. In the Campanularia, which is nearly 

 allied to the Coryne, and in similar polypes, this relation 

 is also very manifest, and in fact resides in an alternation 

 of at least three successive generations, which act 

 reciprocally in connexion wdth each other in the ad- 

 vancing of the species towards perfection. The pheno- 

 menon appears in a striking light, especially in the 

 observations illustrated with figures, for which science 

 has been lately indebted to the Swedish natm^alist S. 

 Loven. The three generations are disposed in a definite 



