342 INSECTA. 



individuals which are again capable of producing seeds or individuals 

 of the primary form, or that to which the plant owed its origin, only 

 by the intervention of a whole series of generations. It is certainly 

 the great triumph of morphology that it is able to show how the plant 

 or tree (that colony of individuals arranged in accordance with a simple 

 vegetative principle or fundamental law) unfolds itself through a fre- 

 quently long succession of generations into individuals becoming con- 

 stantly more and more perfect, until, after the immediately precedent 

 generation, it appears as Calyx and Corolla, with perfect male and 

 female individuals, stamens (Staubblatter) and pistils (Fruchtblatter), 

 and, after the fructification, brings forth seed which again goes through 

 the same course. 



(896.) To facilitate the comparison thus instituted by Steenstrup, 

 Professor Owen has devised the diagrams copied in the opposite figure, 

 which place before the eye the whole of this most interesting subject*. 



(897.) The pollen-tube or filament (fig. 172, l, a) discharged from 

 the pollen-cell (a 1 ) in the plant, represents the spermatozoon (a 2 & 3) 

 in the animal ; its contents (whether by endosmose or perforation is im- 

 material) are received by the ovule (6 l), which is afterwards discharged 

 and becomes free. Under favourable circumstances the formation of 

 the embryo takes place with manifold modifications, but essentially by 

 the multiplication of cells, according to a process which is as much en- 

 titled to be called continuous growth as that process in the formation 

 of the Conferva. The embryo (c) proceeds to develope the radicle and 

 the plumula (d) by the metamorphosis and coalescence of certain of the 

 impregnated cells, retaining the major part, however, as cells ; and thus 

 the first individual plant or pair of individuals, as in Dicotyledons, is 

 established. 



(898.) The ovum (fig. 172, 2, 6) of the zoophyte proceeds to de- 

 velope its free locomotive embryo (c) by an analogous multiplication of 

 cells, certain of which are metamorphosed into an external skin with 

 vibratile cilia ; the embryo settles, subsides, shoots out rays analogous 

 to the radicle of the plant, but for attachment only, and grows after- 

 wards as a stem, from which a polyp (d) is speedily developed, answering 

 to the first cotyledonal leaf or leaves in the plant (fig. 172, l, d). Both 

 plant and zoophyte proceed to develope by gemmation, the one a suc- 

 cession of leaves (e e), the other of polyps (e e) associated by the con- 

 tinuous growth of the connecting parts; and finally the plant, by a 

 metamorphosis of part of the stem and certain leaves, produces the 

 flower or fructification (/, g, h, i) ; and the zoophyte, by a modification 

 also of its stem and certain polyps, produces an "ovarian vesicle" (/), 

 or a modified polyp (g), or a medusiform individual (I), which is set 

 free : in both cases the end to be attained is the diffusion of the species 

 by means of impregnated seeds or ova. 



* Fide Owen, Parthenogenesis, p. 58 et seq. 



