layers of organs, as "the rudiment already before incubation, 

 is composed of two plates or layers, which constitute the 

 layers of all the embryo". The opinion of Reichert was a step 

 backwards, because the refusal of the theory of embryonic 

 plates is at the same time a negative step in the development 

 of lower and higher vertebrates (344) . 



(98) In one of the theses (2) , enclosed in this disser- 

 tation and not connected with its contents, Baer wrote: 

 "Legem a nature scrutatoribus proclamatam evolutionem, quam 

 prima aetate quoque subit animal, evolutioni, quam in animalium 

 serie observandam putant, respondere", a natura alienam esse 

 contendo" (I decide ly confirm that the law, proclaimed by 



the naturalists, "development, inherent from the beginning 

 in a separate animal, corresponds, as it is supposed, to the 

 development, observed in animal series", is alien to nature) . 

 In the commentary on the list of his works ("Autobiography", 

 German edition, p. 607) Baer himself noted that the contents 

 of this thesis is an indication to the beginning of his 

 investigations on the history of animal development (350) . 



(99) Baer cited with bewilderment Erman, who confirmed 

 that the birds eggs could develop in the absence of oxygen 

 (in an atmosphere of hydrogen, nitrogen or carbon dioxide 

 gases) . The importance of atmospheric air for the develop- 

 ment of chicken embryo was demonstrated for the first time 

 by Geoffory St. Hilaire in experiments of varnishing the 



egg shell (E. Geoffory St. Hilaire Memoire sur les differents 

 etats de pesanteur des oeufs au commencement et a la fin de 

 l'incubation, "Isis", 1820, pp. 918-925). 



It was not longer before spectacular results of Erman 

 were disapproved. T. Shvani, under the advice of his teacher 

 log. Mtiller, was dedicated to investigate this question through 

 a doctor dissertation "De necessitate aeris atmosphaerici ad 

 evolutionem pulli in ovo incubato" (Berolini, 1834, 4°) . 

 From which extracts were published in the same year in 

 German: T. Shvani. Uber die Nothwendigkeit der atmBspharischen 

 Luft zur Entwicklung des Huhnchens in Ei, Fror. Not., 41, 

 No. 896, 1834, pp. 241-245. 



At the time of the publication of the second volume of 

 "History of animals development" Baer had stopped his work on 



639 



