ANIMAL METAMORPHOSIS. 87 



wings flit over the surface of their aqueous birthplace ; — transfor- 

 mations more wonderful than those produced by the fairy wand of 

 Cinderella's grandmother. 



We will now consider, as far as space will permit, some of the 

 most striking instances of metamorphosis in the different divisions 

 of the animal world. 



Many of the earlier forms of animal Hfe possess various modes 

 by which the reproduction of the species is effected. The simplest 

 methods are those technically known as " fission " and " gemma- 

 tion," the former of which consists in a gradual division or cleav- 

 age of the body into two parts, each of which then develops into 

 a separate and independent individual exactly like the parent 

 form ; while in the case of gemmation or budding, the animal 

 throws out buds from some part of its body, which, after a more 

 or less complete development into the parental form, are detached 

 to lead a separate existence. Both these processes are non-sexual, 

 and as they are exhaustive to the parent they cannot be carried on 

 indefinitely. In order to ensure the continuance of the species, 

 the sexes must present themselves^ and ova and sperm-cells must 

 be developed and allowed to come into contact with each other. 

 And it is in this mode of development that we meet with the 

 variations we are now considering. 



In the development of the lowest forms of the Protozoa — 

 those minute organisms which appear to exist on the confines of 

 the animal and vegetable kingdoms — in many instances reproduc- 

 tion appears to take place only by gemmation and fission, no 

 differentiated sexual organs having at present been discovered. In 

 these cases, as we have seen, the young immediately grows up into 

 the likeness of the adult, no metamorphosis being apparent, but 

 in others, the changes are so various, that at one period of their 

 life they exhibit an aggregate of phenomena, such as to justify us 

 in speaking of them as animals, while at another they appear to 

 be as distinctly vegetable. This is strikingly the case with some 

 of the Myxomycetes, which were formerly considered as plants, 

 but since the discovery of their life-history it has been proposed by 

 Saville Kent to transfer them from the vegetable to the animal 

 world under the name of Mycetozoa. Here, on the rupture of 

 the spores, the protoplasm escapes, forming uniciliate zoospores, 



