Royal Institution. 63 



two parts. This division is repeated with the same result, until the 

 principle has diffused itself by indefinite multiplication through the 

 whole velk which then constitutes the ' gemi-mass.' 



The' next stage is the formation of the embn'o : certain of the 

 minute subdivisions called ' nuclei ' or nucleated cells, combine and 

 coalesce to constitute the tissues of the embryos : they are afterwards 

 incapable of generating. If all be so metamorphosed, the organism 

 cannot procreate of itself; but if a part only of the germ-mass be 

 metamorphosed into tissues, the unchanged remnant may, if nutri- 

 tion, heat, and other stimuli are present, repeat the same actions as 

 those that formed the first germ-mass, and lay the foundation of 

 future embryos. 



In proportion to the amount of the substance of an organism 

 which retains the primitive condition of cells, is the power of pro- 

 ducing new individuals without receiving a fresh supply of the pollen- 

 principle. 



Thus in a plant, when the seed has received the matter of the 

 pollen-filament, analogous changes take place to those that have 

 been described in the animal egg, and the embryo plant appears 

 in the form of the cotjledonal leaf with its radicle or rootlet. From 

 this shoots forth another leaf with its stem : and the cellular sub- 

 stauce of the pith with its share of the pollen-principle goes on 

 developing fresh leaves and leaf-stalks ; until a pro^-ision for de- 

 veloping fresh poUen is made by transforming certain individual 

 leaves into a higher form of the 'phyton' or elemental plant. Thus 

 a generation or ' whorl ' of leaves assumes the character of sepals, 

 another that of petals, a third that of stamens, a fourth that of 

 pistils : and in the two latter forms we recognise the analogues of 

 the perfect male and female of the animal. 



The development of the compound polype follows very closely 

 the stages of the compound plant, which we call shrub or tree : 

 the ovum, hke the seed, having received the pollen-principle, is 

 converted into countless cells and nuclei of cells by the process for 

 diffusing that principle through, or of assimilating it with, the matter 

 of the egg. Then certain germ-cells are metamorphosed into a 

 cihated integument, and the larva starts forth in a state answering 

 to the cotyledonal leaf of the plant : the ciliated larva settles, 

 subsides, and shoots up a stem from which a digestive polype is 

 developed, answering to the leaf: but the pollen-force not being 

 exhausted, a second branch and polype are developed, and so on 

 until a preparation is made for a fresh supply of pollen-force, by 

 metamorphosing the polype into a higher form of individual ; and 

 this, in many compound polypes, is set free in the shape of a 

 minute medusa. 



The true nature and relation of the individual polype to the 

 compound whole is well illustrated by the propagations of the 

 Aphides. 



By comparing with the diagrams of the metagenesis of the plant 

 and polype, that of the Aphis, in which was represented the corre- 

 sponding stages intervening between the ovum and the perfect male 



