Professor Owen on Metamorphosis and Metagenesis. 275 



analogy between these stages in the plant, the polype and 

 the insect, was shewn to be both true and close. The mi- 

 croscopic seminal filament of the male Aphis answers to the 

 microscopic pollen filament of the male leaf or *' stamen." 

 The ovum of the female Aphis to the ovule of the female leaf 

 or pistil : by their combination the fertile ovum results. The 

 same process of cell-formation ensues, and the embryo Aphis 

 is formed by the combination and metamorphoses of certain of 

 these secondary germ-cells ; but it retains the rest un- 

 changed in its interior, which may be compared with the 

 cells of the pith of the plant, and with the cells in the cor- 

 responding more fluid part of the pith of the polype. Under 

 favourable circumstances of nutriment and warmth, certain 

 of these cells repeat the process of embryonic formation, and 

 a larval individual like that from the ovum is thus repro- 

 duced ; which is only not retained in connection with its 

 parent, because the integument is not co-extended with it. 



The generation of a larval Aphis may be repeated from 

 seven to eleven times without any more accession to the 

 primary pollen-force of the retained cells than in the case of 

 the zoophyte or plant ; one might call the generation, one by 

 *' internal gemmation," but this phrase would not explain the 

 conditions essential to the process, unless we previously 

 knew those conditions in regard to ordinary or external gem^ 

 mation. 



At length, however, the last apterous or larval Aphis, so 

 developed, proceeds to be " metamorphosed" into a winged 

 individual, in which either only the fertilizing filaments are 

 formed, as in the case of the stamens of the plant, or only 

 the ovules, as in the case of the pistil. We have, in fact, at 

 length "male and female individuals," preceded by procreative 

 individuals of a lower or arrested grade of organization, ana- 

 logues to the gemmiparous polypes of the zoophyte and to 

 the leaves of the plant. 



The process was described for its better intelligibility in 

 the Aphides as one of a simple succession of single indivi- 

 duals, but it is much more marvellous in nature. The first- 

 formed larva of early spring procreates not one but eight 

 larvsB like itself in successive broods, and each of these larvsa 



s2 



