604 



FABIOLA MÛLLER 



SUMMARY OF PART III 



1. Among primitive Eutheria, the succession of events in the somatic deve- 

 lopment is not altered by évolution from the nidicoloiis to the ^v\m\i\\Q Eutheria- 

 nidifuge type. In the simplest case (Acomys cahirimis) the passage from the one 

 ontogenetical type to the other is a resuit of the longer intra utérine period. 



2. A modified chronology of somatic development appears in the highly 

 cerebralized Eutheria, which usually are of the nidifuge type. The différent deve- 

 lopmental phases (except that preceeding the implantation) are prolonged in 

 comparison the those of the primitive forms. Somatic differentiation is spread 

 over a longer period. 



Most of the highly cerebralized Eissipedia have kept the nidicolous state. The 

 interval which séparâtes their already highly differentiated newborns from the 

 maturity level of nidifuges is comparatively small. 



The rule of precedence by Portmann means that a higher degree of cerebra- 

 lization only takes place in nidifuges; this is due above ail to the longer duration 

 of intrauterine development, which is necessary for an increase of the brain mass. 

 The particular succession of différent ontogenetical types found in the mammalian 

 lineage fiom the reptiles may also correspond to the modifications of the develop- 

 ing time. 



3. Altered chronologies, as found in the highly cerebralized Eutheria, 

 already exist in some primitive mammals. In thèse mammals, both brain and body 

 development are deiayed; their odds of further évolution seem reduced. Hetero- 

 chronies observed in some 'of thèse deiayed types are presented. 



LITERATUR 



Adams, L. E. 1903. A contribution to our knowledge of the mole Talpa europaea. Mem. 



Manch. Lit. Phil. Soc. 47: 1-39. 

 — 1909. Some notes on the breeding habits of the common mole. Mem. Froc. Manch. 



Lit. Phil. Soc. 54: 1-9. 

 Addison, W. et H. How. 1921. The development of the eyelids of the Albino Rat until 



the compleiion of disjunction Am. J. Anat. 29: 1-33. 

 Althaus, p. 1937. Zur Ontogenie des Centetes-Gebisses. Med. dent. Diss., Bern. 

 Altner, g. 1968. Histologische und vergleichend-anatomische Untersuchungen zur 



Ontogenie und Phylogenie des Handskeletts von Tupaia glis ( Diard 1820) 



und Microcebus murinus (J. F. Miller, 1777). Inaug. Diss., Giessen. 

 Anders, j. 1924. Untersuchungen iiber das Auftreten und die weitere Entwicklung der 



embryonalen Hirnschàdelknochen des Schweines. Morph. Jb. 53 : 259-303. 



