64 Royal Institution. 



and female indmduals of the Aphis, the analogy between these 

 stages in the plant, the polype, and the insect, was shown to be 

 both true and close. The microscopic fertihzing 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 processes of cell-formation ensue, and the embryo Aphis 

 is formed by the combination and metamorphoses of certain of 

 these secondary germ-cells ; but it retains the rest unchanged in its 

 interior, which may be compared with the cells of the jnth of the plant, 

 and with the cells in the corresponding 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 reproduced; 

 which is only not retained in connection Avith its parent, because the 

 integument is not coextended vrith 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 gemmation. 



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

 loped, 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 indi- 

 viduals,' preceded by procreative individuals of a lower or arrested 

 grade of organization, — analogues 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 individuals, but it is 

 much more marvellous in nature. The first-formed larva of early 

 spring procreates not one but eight larvse like itself in successive 

 broods, and each of these larvae repeats the process ; and it may be 

 again repeated in the same geometrical ratio until a number which 

 figures oidy can indicate and language almost fails to express, is the 

 result. The Aphides produced by this internal gemmation are as count- 

 less as the leaves of a tree, to which they are so closely analogous. 



It generally happens that the metamorphosis which has been 

 described as occurring after the seventh or eleventh generation takes 

 place much earlier in the case of some of the thousands of indi- 

 viduals so propagated ; just as a leaf-bud near the root may develope 

 a leaf-stem and a flower with much fewer antecedent generations of 

 leaves from buds than have preceded the formation of the flower at 

 the summit of the plant ; or just as one of the lower and earlier-formed 

 digestive polypes may push out a bud to be transformed into a pro- 

 creative and locomotive polype. The same analogy is closely main- 

 tained throughout. 



