Protoplasmic Streaviing — Relation to Gel Structure 141 



As soon as the pressure is released the furrow recedes no further, 

 and within less than a minute it begins to push inward once more 

 toward the axis. The delayed furrowing now continues rapidly to 

 completion, provided that the pressure inhibition has not been main- 

 tained for more than 14 or 15 minutes.-"^ No injury appears to result 



A 



mn 



B 



Fig. 5. The setting of the cortical gel of the Arbacia egg, which occui'S just 

 prior to the appearance of the cleavage furrow. A, two unfertilized eggs, and B, 

 a fertilized egg 5 minutes before cleavage time, all centrifuged together for 6 

 minutes at atmospheric pressure. The greater rigidity of the cortical gel of B 

 is indicated by the fact that there has been scarcely any displacement of the 

 pigment granules, which in this egg (Arbacia piLstulosa) are localized entirely 

 in the cortex. Note that the undisplaced pigment is readily observable in the 

 cortical part of the hyaline zone. 



from the temporary suppression, for the eggs continue to develop 

 in an apparently normal fashion. They go through the second and 

 third cleavage at the same time as control eggs, and give rise to 

 blastulae which cannot be distinguished from untreated specimens. 

 (4) Ejfect of pressure on the rate of furrowing 



In view of the marked effect of the relatively high pressure, it 

 was of interest to determine how cleavage might be modified by 

 lesser degrees of constraint. Soon it became apparent that lower 



