STAMMESGESCHICHTLICHE VERÀNDERUNG DER EUTHERIA-ONTOGENESEN 1657 



to which belong the Rodentia. Insecth ora, Xenanhra, Prosimiae and Fissipedia, 

 \ve find numerous ontogenetic types; in the second one, containing Siniiae, 

 Ungulata, Proboscidea and Piimipedia and in which the évolution of brain 

 reaches a high degree, we find as only ontogenetic type the nidifugeous new- 

 born. Table 17 shows that évolution from the nidicole to the nidifuge type 

 consists of altérations of somatic maturation in the newborn. The phylogenesis 

 of the nidifuge however consists of an increase of the brain mass. Among the 

 Sciurumorpha and Fissipedia we find some exceptions to Portmann's rule of 

 precedence. 



2. The comparative study of embryos at the stage immediately foUowing eyelids 

 closure allows the following constatations. 1. About their length: 15-30 mm 

 CR-lengths are found in the Rodentia, Insectivora, Xenarthra, Siniioe. How- 

 ever the embryos of Carnivora are 40 mm. those of Urigiilata. Proboscidea and 

 Cetacea about 60 mm long. The embryos of Chiroptera have a length of only 

 12-15 mm CR. We have probably to deal hère with an adaptation to the flying 

 life. 2. The young embryos at the stage immediately following eyelids closure 

 already show the characteristics of their systematic group. Figure 8 calls 

 particular attention to Elephas maximus, Balaenoptera physahis and Rhinocéros 

 africanus. 



3. In our first part, we found in the Insectivora and Rodentia a primitive pattern 

 of the developmental timing in the différent parts of the body. This fact is in 

 accordance with our latest literature findings concerning the Lagoniorpha, 

 Chiroptera and Fissipedia. Among the Xenarîhra and Arfiodacfy/a, hetero- 

 chronies are found. The Cetacea, Sirenia and Pinnipedia are not yet known 

 from this point of view. 



4. The évolution from nidicole to nidifuge type consists of a postponement of 

 birth. The phylogenesis from primitive to highly cerebralized Eutheria is 

 however prepared by a prolongation of each of the embryological periods. 



5. Moreover there are some groups with poorly developed brain masses presenting 

 the same altered chronologies as those found in the highly cerebralized Eutheria. 

 We find such cases among the Rodentia. Insectivora, Chiroptera. Xenarthra. 

 Mustelidae and Prosimiae. 



6. In the ontogenetic type which is called "secondary nidicole" by Portmann, 

 birth occurs very soon after opening of the eyelids. We find it in the Siniiae 

 and Xenarthra and also perhaps among some Pholidota. 



7. Highly cerebralized nidicoles are found among the Fissipedia. Sciurumorpha 

 and perhaps among some Prosimiae. 



