PAKTHENOOENESIS. 



343 



(899.) Now if we compare fig. 172, 3, in which are represented 

 the corresponding stages intervening between the ovum and the perfect 

 male and female individuals of the Aphis, with fig. 172, 1 & 2, the 

 analogy between these stages in the plant, the polyp, and the insect 

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

 male Aphis Qi) answers to the pollen- filament (fig. 172, 1, a} of the 

 male leaf or stamen (h). The ovum (6) of the female Aphis (i) 



Fig. 172. 



ft* 



Comparative view of the reproductive process in a Plant, a Campanularian zoophyte, and a female 

 Aphis, the corresponding parts being indicated by similar letters, as explained in the text. 



answers to the ovule (6) 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 (cZ) is formed by the com- 

 bination and metamorphoses 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 in the plant, and with the cells or 

 nuclear granules in the corresponding more fluid part of the pith of the 

 polyp. Under favourable circumstances of nutriment and warmth, 

 certain portions of the retained germ-mass repeat the process of em- 



