Fig 142 Early development of Rana pipiens. (A) Polar view of first cleavage. The 

 animal pole is considerably flattened at this time and tension lines are visible extending 

 outward along either side of the furrow. (About VA hours after fertilization in the 

 laboratory, room temperature 20 to 22° C.) (B) First cleavage furrow a little later 

 (C) First furrow proceeds slowly though the yolk of vegetative (vegetal) pole. (U) 

 Second cleavage furow meridional and at right angles to the first furrow. (E) Four-cell 

 stage, view from animal pole. Observe short "cross furrow" connecting first and second 

 cleavage planes. (F) Fourth cleavages meridional or nearly so. Taken from egg spawned 

 in nature. Considerable variation may exist. Some cleavages may be vertical and not 

 meridional. (G-1) Later blastula stage. (J) Stage just before appearance of dorsal 

 lip of blastopore. (K) Dorsal lip of blastopore. (L) Yolk-plug stage of gastrulation. 



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