CONTENTS. 



Introduction. 



A. Organization of the Egg 



B. Ascidian Embryology 



C. Methods and Material 



1. The Ovarian Egg. 



1. Development of the Ovocyte 



'2. Test Cells and Chorion . 



3. Structure of Fullv Formed Ovocyte 



II. Maturation and Fertilization. 



A. Maturation ..... 



1. Disappearance of Nuclear Membrane 



2. Chomosomes .... 



3. Nucleolus ..... 



4. Spindle Formation 



5. Movements of Spindle and Nuclear Plasm ; Formation of 



B. Fertilization ..... 



1. Entrance of Spermatozoon 



2. Movements of Ooplasm 

 a. Localization of Yellow Protoplasm 

 1). Localization of Clear Protoplasm and Yolk 



3. Development of Sperm Nucleus and Aster 



4. Path of Spermatozoon within the Egg . 

 5- The Egg Nucleus and its Movements 



6. Sperm Amphiaster and First Cleavage Spindle 



7. Dispermy ....... 



Polar Bodies 



III. Orientation of Egg and Embryo. 



1. Van Beneden and Julin's System of Orientation 



2. Seeliger's System ....... 



3. Samassa's System ...... 



4. Castle's System ....... 



5. Evidences in Favor of Van Beneden and Julin's System 



IV. Cell-Lineage. 



A. Nomenclature ....... 



B. Cleavage of the Egg ; First to Seventh Generation of Cells 



1. First Cleavage ; 1-2 Cells 



2. Second Cleavage ; 2-4 Cells . 



3. Third Cleavage; 4-8 Cells . 



4. Fourth Cleavage; 8-16 Cells 



5. Fifth Cleavage ; 16 32 Cells 



6. Sixth Cleavage ; '!2-64 Cells 



C. Gastrulation ; Seventh to Ninth Generation of Cells 



7. Seventh Cleavage; (54-76 Cells, 76-112 Cells . 



8. Eighth Cleavage ; 112-132 Cells, 132-218 Cells 



9 



10 

 10 



13 

 13 

 14 

 15 

 15 

 17 



18 

 19 

 19 



20 

 22 

 22 

 23 

 23 

 24 



26 

 27 



28 

 28 

 32 



37 

 39 

 39 

 43 

 44 

 48 

 5o 

 53 

 60 

 60 

 65 



