I 



cleavage (Segmentation) and Blastulation 



A. General considerations 



1. Definitions 



2. Early history of the cleavage (cell-division) concept 



3. Importance of the cleavage-blastular period of development 



a. Morphological relationships of the blastula 



b. Physiological relationships of the blastula 



1) Hybrid crosses 



2) Artificial parthenogenesis 



3) Oxygen-block studies 



4. Geometrical relations of early cleavage 



a. Meridional plane 



b. Vertical plane 



c. Equatorial plane 



d. Latitudinal plane 



5. Some fundamental factors involved in the early cleavage of the egg 



a. Mechanisms associated with mitosis or cell division 



b. Influence of cytoplasmic substance and egg organization upon cleavage 



1) Yolk 



2) Organization of the egg 



c. Influence of first cleavage amphiaster on polyspermy 



d. Viscosity changes during cleavage 



e. Cleavage laws 



1 ) Sach's rules 



2) Hertwig's laws 



6. Relation of early cleavage planes to the antero-posterior axis of the embryo 



B. Types of cleavage in the phylum Chordata 



1. Typical holoblastic cleavage 



a. AmphioxLis 



b. Frog (Rana pipiens and R. sylvatica) 



c. Cyclostomata 



2. Atypical types of holoblastic cleavage 



a. Holoblastic cleavage in the egg of the metatherian and eutherian mammals 



1 ) General considerations 



2) Early development of the rabbit egg 



a) Two-cell stage 



b) Four-cell stage 



c) Eight-cell stage 



d) Sixteen-cell stage 



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