STUDIES IN THE DEVELOPMENT OF THE OPOSSUM 

 DIDELPHYS VIRGIANA L. 



I. HISTORY OF THE EARLY CLEAVAGE 

 II. FORMATION OF THE BLASTOCYST 



CARL GOTTFRIED HARTMAN 



Contribution fruni the Zoological Laboratory of the University of Texas, No. 126 



SIX TEXT FIGURES AND ELEVEN PLATES 



CONTENTS 



PART I. HISTORY OF THE EARLY CLEAVAGE 



L Introduction 2 



a. Statement of the problem 2 



b. Review of the literature 3 



1) The work of Caldwell and Selenka 3 



2) Cleavage and blastocyst formation in Dasyurus as described 



by Hill ~ 6 



c. Material and technique 9 



1) Material 9 



2) History of the animals 10 



3) Securing of the eggs 12 



4) Fixing and staining 14 



2. Maturation and fertilization 15 



a. The mature ovarian ovum 15 



b. The tubal ovum 16 



c. Appearance of young uterine eggs 19 



d. The pronuclear stage 21 



3. The first cleavage 22 



a. The first cleavage spindle 22 



b. The 2-celled stage 23 



c. The elimination of yolk 23 



4. The 4-celled stage 24 



a. The oi'ientation of the blastomeres 24 



1) Shifting of the blastomeres 24 



2) Consequences of shifting of blastomeres 27 



b. Selenka's 4-celled stage 28 



c. The distribution of yolk 28 



1 



JOURNAL OF MORPHOLOGY, VOL. 27, NO. 1 

 MARCH, 1916 



