STAMMESGESCHICHTLICHE VERANDERUNG DER EUTHERIA-ONTOGENESEN 557 



élevée ne diffèrent pas des nidifuges dans leur développement cérébral. Les seules 

 particularités semblent être un facteur de multiplication très élevé à la naissance 

 et une structuralisation précoce du cervelet médian 



5. La synthèse des données morphologiques et fonctionnelles met en évi- 

 dence le fait que, chez les formes peu cérébralisées, l'ouverture des yeux introduit 

 l'état adulte; chez les Eutheria hautement cérébralisés elle introduit une nouvelle 

 étape importante du développement avec formation intensive de synapses. 



SUMMARY OF PART II 



1. For a comparative study of the development of the brain and of the 

 ontogenetic types, closing of the eyelids and opening of the eyes are seen to be 

 particularly important stages. At the closing of the eyelids, a characteristic corré- 

 lation exists between the structure and the topography of Bulbus olfactorius, 

 hémisphères and Cerebellum. This corrélation is independent of morphological 

 characters and of the adult brain mass. 



2. We have found relatively few bibliographical data about the stage of 

 eye-opening. Hovv^ever our material shows two important facts: a) the stratifi- 

 cation and structuration of neurocytes are adult-like in the olfactory bulbs, the 

 retina, the neocortex and the médian Cerebellum. b) There is négative corréla- 

 tion between the TI value and the speed of development in the cortical dendrites 

 of the brain and in their spines, for a given species. 



3. From the literature it can be deduced that a similar négative corrélation 

 exists between the TI value and the maturation speed of the motility. In the nidi- 

 coles and nidifuges with différent cerebralisation levels the maturation of motility 

 is slower when the TI of the species is higher. Our bibliography shows that, in 

 some primates, birth occurs a shortly after eye-opening. At this stage motor 

 maturation has hardly begun. 



4. Exceptions to the rule of precedence of Portmann are discussed, taking 

 as example the Ursidae. It follows that thèse highly cerebralized nidicoles do not 

 differ essentially from the nidifuges in their cérébral development. A very high 

 multiplication factor at birth and perhaps an earlier structuration of the médian 

 Cerebellum would be particularities. 



5. The synthesis of the morphological and functional facts puts into évi- 

 dence the fact that the eye-opening introduces the adult stage in poorly cerebra- 

 lized species; in the highly cerebralized Eutheria eye-opening introduces a new 

 step of development with intensive formation of synapses. 



