DOUGLAS MARSLAND 



115 



Temperature Effects. The data plotted in figures 2 and 3 show that 

 the cortical plasmagel of the egg cell may be characterized as the type 

 of system in which the structural strength of the gel net-work increases 

 exponentially as the temperature is raised. This applies not only to the 

 relatively weak gel system of the unfertilized egg (fig. 2) but also to 

 the strongly fortified gel of the furrowing egg (fig. 3), where much 

 higher centrifugal forces were required to achieve a displacement of the 

 embedded chromatophores even though fairly high pressures were em- 

 ployed to bring the gel strength down into a measurable range. 



Correlated apparently with this action of temperature in fortifying the 

 structure of the plasmagel system, the furrowing strength of the egg be- 



LBS/SO.IN. 



,'''4ooa 



Fig. 3. Plasmagel strength in 

 relation to temperature at vari- 

 ous pressures. Measurements 

 made on cleaving eggs of Ar- 

 bacia lixiiln. Data from Mars- 

 land and Landau, 1954. 



lU 



I- 



< 

 o 



cc 



h- 

 z 



UJ 



o 

 I 



X 



I- 

 o 



z 



UJ 



a: 



MINIMUM GEL STRENGTH FOA'' FURROWING 



400 



300 



200 



100 

 60 



.60 



6000 



eooo 



,'' 10000 



,'' 12000 



ARBACIA LIXULA 



10 e 20 



TEMPERATURE, 'C 



2» 



comes progressively greater at higher temperatures — as may be seen in 

 figure 4. Thus with each increment of 5°C, the magnitude of the pres- 

 sure reciuired to block the furrows becomes greater — by about 1,000 

 lb/in.- for the eggs of Echinarachnius and Arbacia — and by about 500 

 lb/in.- for the Amphibian and Annelid eggs. Moreover, the correlation 

 between gel structure and furrowing strength becomes even plainer in 

 light of the data shown in figure 5. This family of curves shows that a 

 furrowing block occurs whenever the structural strength of the cortical 

 gel system falls to a certain critical level. At higher temperatures the 

 pressures required to produce this critical weakening are higher, and at 

 lower temj^eratures they are lower; but in each case the cell is rendered 

 incapable of performing the work of cleavage by any combination of tem- 

 perature and pressure treatments that weakens the gel structure to approxi- 

 mately the same degree. 



