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which until his time had been e inexplicable 5 ; quite un- 

 conscious, apparently, how little the term ' alternation of 

 generations/ and the figurative expression of ' wet-nurse/ 

 applied to the fertile larval stage of an animal, serve to 

 acquaint us with the nature or essential conditions of the 

 phaenomena. And I may further observe, that if it were 

 proved that the ( multiplication of cells by a process of con- 

 tinuous growth, with independent vitality,' was a process 

 altogether distinct from that multiplication of cells in an 

 ovum which precedes the formation of the tissues of the 

 embryo ; yet the words e multiplication of cells, with or 

 without continuous growth/ would equally leave us devoid 

 of the idea of the essential force and condition of structure 

 that make the development of a young animal from a larval 

 polype or a wingless virgin Aphis possible. And we are 

 interested to learn, therefore, what that may be which the 

 reviewer calls " our philosophical interpretation of this won- 

 derful process " (p. 203). He truly compares the fertilized 

 ovum of the medusa-parent to the seed of the plant, the 

 polype that grows from it with its progeny by gemmation 

 to leaf-buds, and those discoid portions developed between 

 the base and summit of the Strobila to flower-buds. For 

 these discoid segments, in point of fact, when separated, 

 become either male or female Medusa3, and developing the 

 generative organs, justify the above comparison. The re- 

 viewer says, " It is evident to us that the pile of medusa- 

 discs is not formed by the constriction of the proper body 

 of the original polypoid animal;" yet he afterwards states 

 that the detachment of those discs " involves the separa- 

 tion of the tentacular ring from the body at the base/' 

 that it separates one end of the polypoid animal from the 

 other, which implies something more than constriction, 

 constriction, viz. carried to the extent of absolute fission of 

 the original polypoid animal. But this fission is preceded, 

 as in the Nais and Nereis, by gemmation of the part to be 

 separated thereby. 



