Proto-plasmic Streaming — Relation to Gel Structure 143 



furrows were expected-'" to appear, at which time the pressure was 

 raised quickly to the desired level. In order to time the progress of 

 the intruding furrow accurately, it was found necessary to remove 

 the fertilization membranes by shaking the eggs before placing them 

 in the chamber. This procedure permits the dividing eggs to become 

 more elongate in the direction of the division axis and enables one 

 to see the furrows more plainly. In this way it is possible to deter- 

 mine precisely when the furrow begins to form and when it finally 

 reaches the axis of the dividing cell. 



As the pressure is increased there is a marked increase in the 

 time required for the furrow to complete its passage from the equator 

 to the axis. At 2,000 lbs. /in.- the rate of progress of the furrow is 

 only half the atmospheric rate,-' whereas at 5,000 lbs. the progress 

 is slowed to about one-fifth of the original rate. At pressures between 

 5,000 and 6,000 lbs., abortive furrows are formed which fail to reach 

 the division axis before receding. Above 6,000 lbs. no furrows 

 appear although the eggs do become slightly elongate at the time 

 when cleavage is due. 



When one plots the rate of furrowing as a function of pressure 

 (Fig. 2) , it becomes apparent that the retardation is in proportion to 

 the solation effect which the pressure exerts upon protoplasmic gels 

 generally. This would indicate an intimate relation between the 

 mechanics of furrowing and the capacity of the plasmagel system 

 to undergo a process of setting at the time when the furrowing is 

 active. However, direct measurements of the pressure effect upon 

 the exceptionally stiff gel which is formed at this critical time, 

 remain for consideration. 

 (5) Solation of the firm "cleavage gel" 



The eggs of Arhacia pustulosa, which are available at the Naples 

 laboratory in adequate quantities throughout the year, were chosen 

 for these experiments. These eggs possess an unusually generous 

 number of pigment granules, and this pigment is confined, even in 

 the unfertilized egg, almost entirely to the cortical layer of the 

 cytoplasm. These two attributes are of particular advantage in the 

 experiments. 



Heretofore, it had not been possible, using centrifugal forces 

 up to 7,200 X gravity, and pressures up to 7,000 Ibs./in.- (Brown, 

 '34c) , to cause any appreciable displacement of the pigment granules 

 if the centrifuging were done late in the division cycle, i. e., within 

 10 minutes of the time when the furrows were due to appear. In 



