220 THE THEOKY OF EVOLUTION 



in the embryogeny of many organisms, Hackel 

 does not know that the Mammals were once fish or 

 tadpoles ; in them, therefore, he has no c norm ' for 

 what is ( lacking ' or ' falsified/ l 



(b) The logical extension of the principle leads 

 to quite untenable consequences, or it proves, if these 

 consequences be avoided, nothing more regarding the 

 origin of the types (Birds and Mammals for instance). 



A simple consideration will convince us of this. 

 In the individual genesis of a present-day bird there 

 arises, as experience shows, a hard-shell egg stage which 

 is usually termed a c bird's egg/ This bird's egg is not 

 to be confounded with the actual female germ cell 

 which scientifically is generally termed egg (or egg 

 cell). The germ cell is originally a microscopically 

 small cell which quite early accumulates in the proto- 

 plasm yolk particles for the nourishment of the future 

 embryo and thus forms the ' yolk/ This yolk is the 

 fertilizable female sexual cell ; only after fertilization, 

 when traversing the oviduct, are further coatings added 

 the material for which is supplied by glands viz. 

 the albumen (white of egg), then a fine double egg skin 

 (directly under the lime shell and detachable), and 

 finally the hard lime shell. Thus is the egg finally ' laid/ 

 The germ cell alone, or already in the form of a germ 

 stage, is thus enclosed in the egg when laid. 3 



1 That palaeontology also gives no ' norm ' we shall soon see. 



2 An ' embryo ' (germlet) is then, strictly speaking, already present if 

 the single cell stage is no longer there i.e. after the first ' division ' (= divi- 

 sion of the developing egg). Usually certainly the term ' embryo ' is 

 only applied to more advanced stages. 



