CLEAVAGE 



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Cleavage in Amphibia. — These ova contain so much yolk that the nucleus 

 and most of the cytoplasm lies at the upper or animal pole. The first cleavage 

 spindle Kes in this cytoplasm. The first two cleavage planes are vertical and at 



4 5 



Fig. 16. — Cleavage of the frog's ovum (Hatschek in Marshall). X 20. B, Blastoccele or cleavage cav- 

 ity; N, nucleus. 



right angles, and the four resulting cells are nearly equal (Fig. 16, 1). The 

 spindles for the third cleavage are located near the animal pole and the cleavage 

 takes place in a horizontal plane. As a result, the upper four cells are much 

 sriialler than the lower four (2 and 3). The large yolk-laden cells divide more 



