EMBRYOGENY 



225 



of its entire essence. The parent animal produces, how- 

 ever, no amoeba but reproduces its own form. Each 

 germ stage is through and through a mammal in the 

 making, devoted to that one object by the preceding 

 stage and itself determining the succeeding one to the 

 same end. 1 The types have thus experienced no 

 greater alteration in their embryogeny than in their 

 grown condition, which in all cases is only the result of 

 germ stages determined in one particular direction. 

 Since, however, the types to the eye whether accord- 

 ing to present systematic classification or according 

 to palaeontological finds as adult mammals never 

 show any association with any other class whatever, 

 therefore also the embryonic stages can present no 

 approximation since they belong to the complete 

 condition and produce it. 



(d) As regards the applicability of the ' biogenetic 

 basal principle ' in palaeontology Zittel stated in 

 1895 at the International Geological Congress : ' If 

 palaeontology be consulted, it must be recognized that 

 this hypothesis has not been confirmed in any way/ 

 He then shows by several examples at what ' peculiar 

 ancestors ' we must arrive according to the ' basal 

 principle ' for instance, for the Crinoids (Hairstars) 

 and Sea Urchins, which, however, ' would not accord 

 in the remotest degree with the facts/ Such examples 



i All this has been determined by modern biologists by observation 

 and experiment. See, for instance, Driesch : Philosophic des Organischen, 

 I, p. 76; Analytische Theorie der Formbildung, Korschelt and Herder, 

 part I, p. 81 ; Das Determinationsproblem ; O. Hertwig : Allgemeine 

 Biologic, p. 572, ' Die Theorie der Biogenesis' 



Q 



