116 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



General Interpretation. The temperature-pressure data (figs. 2-5) in- 

 dicate that there is a quantitative relationship between the gclational 

 state of cortical plasmagel layer in the equatorial region of the dividing 

 cell and the strength of the furrowing reaction. Recent workers, indeed, 



10 



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FURROWS RECEDE 



7 



FURROWS ADVANCE 



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10 15 20 25 30 35 *C 



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Fig. 4. Temperature variations in tlie minimum pressure required to block the first 

 cleavage furiow in several different eggs. Data from Marsland and Landau, 1954. 



are generally agreed that a decisive role in cytokinesis is played by the 

 cortical plasmagel layer of the cyto])lasm. However, there is no agreement 

 as to the precise mechanism of the furrowing process. In fact, two opposite 

 viewi)oints are currently held: jirst that the cell membrane is pushed 

 down into the developing furrow by a process of 'growth' (30, 3) or of 

 'expansion' (31, 26) occurring in the cortical protoplasm; and second, 



