59 



stages intervening between the ovum and the perfect male 

 and female individuals of the Aphis, the analogy between 

 these stages in the plant, the polype and the insect, will 

 be seen to be both true and close. The spermatozoon (a) of 

 the male Aphis (h) answers to the pollen-filament (0, fig. 1) 

 of the male leaf or ' stamen' (h). The ovum (b) of the 

 female Aphis (i) answers to the ovule (b) of the female leaf 

 or pistil (i): by their combination the impregnated ovum 

 results. The same processes of cell-formation ensue, and 

 the embryo Aphis (d) is formed by the combination and me- 

 tamorphoses of certain of these secondary germ-cells ; but 

 it retains the rest as a germ-mass in its interior, which may 

 be compared with the cells of the pith of the plant, and with 

 the cells or nuclear granules in the corresponding more 

 fluid part of the pith of the polype. Under favourable 

 circumstances of nutriment and warmth,, certain portions 

 of the retained germ-mass repeat the process of embryonic 

 formation, and a larval individual (e, fig. 3) like that from 

 the ovum is thus reproduced ; which is only not retained 

 in connexion with its parent, because the abdominal inte- 

 gument is not coextended with it. 



The generation of a larval Aphis may be repeated from 

 seven to eleven times without any more accession to the 

 primary spermatic virtue of the retained germ-masses than 

 in the case of the zoophyte or plant : one might call the 

 generation an e 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 

 developed, proceeds to be f metamorphosed,' as it is termed, 

 into a winged individual, in which only the fertilizing fila- 

 ments are formed, as in the case of the stamens of the 

 plant (h) ; another larval Aphis (i) perfects the female ge- 

 nerative organs* and developes the ovules, as in the case 



* This is not attended by the acquisition of wings ; or, if they be de- 



