IN THE ANIMAL KINGDOM. 107 



§ 12. An observation that suggests itself in comparin*-'- 

 the reproductive process in the several groups of Animals, 

 as represented in the preceding summary, with the modifi- 

 cations of the same functions ,of Veo-etables, is the sino-ular 

 difference of the general result in the two kingdoms, aris- 

 ing from the same general law of the interpolation of gem- 

 mation at certain points in the genetic cycle. Its effect in 

 the case of plants is to establish a wide apparent diversity 

 between the reproductive process of the higher and the 

 lower cryptogamic plants ; while in animals it is rather 

 to bring forward, in the case of particular families or 

 species, a series of forms, which, however apparently dis- 

 similar, are really only successive phases of one individual, 

 or detached offshoots or members of the same orioinal stock. 



Very much of the general character of the reproductive 

 process in any family depends on the mutual relations of 

 certain epochal acts, as they may be called — such as access 

 of the spermatic element (Insemination=I) ; discharge of 

 the ovum or its contents (Extrusion=E) ; escape of the 

 young from the egg coverings (Birth=B) ; and the full 

 acquisition of the typical characters (Development^D). 

 The follomng tabular statement, therefore, in which these 

 acts are denoted by the letters above indicated, may be of 

 interest, as showing some of the more usual variations, in 

 their order of succession, in the different tribes of animals. 

 When two letters follow each other immediately, it denotes 

 that the acts are simultaneous ; the interposition of a 

 greater or less number of points indicates a corresponding 

 interval of time in the succession : — 



Mammalia I DEB 



Marsupialia I...EB D 



Birds I.E DB 



Batrachia EI...B D 



Fishes E.I...B D 



Insects LE...B D 



