408 E. E. JUST. 



much higher degree of fluidity than bef ore " (Lillie, '06, page 

 176). " The strongest evidence for greater fluidity at this time is 

 found in the fact that the ectoplasmic spherules are much more 

 numerous and smaller than they were previously or than they are 

 subsequently. Evidently there is a reversible process of coagula- 

 tion concerned, the spherules breaking down into smaller particles 

 as the fluidity increases and setting or coagulating again by a 

 process of fusion." 



"If eggs are allowed to stand eight to fifteen minutes in sea- 

 water after being taken from the female so that in some the 

 germinal vesicle is intact and in others broken down, the latter 

 always show stratification more or less pronounced after centri- 

 fuging and the former never show it. ... It would seem that the 

 endoplasm has become less viscid as a result of the diffusion of 

 substance from the germinal vesicle so as to permit of a closer 

 aggregation of the yellow granules." 



Let us, however, waiving this demonstration of a difference in 

 the physical make-up of the cortex and endoplasm of the unferti- 

 lized Cluctoptcrus egg, as well as Chambers's observation that the 

 gelation succeeding insemination is localized in the region of the 

 sperm aster, assume that in the Arbacia egg a gelation follows the 

 liquefaction of the cortex. But the viscosity theory of fertiliza- 

 tion is not thus made more tenable. 



According to the viscosity theory (Heilbrunn), initiation of de- 

 velopment by artificial agents or by sperm involves coagulation of 

 the eggs ; the mitotic spindle probably arises as a direct result of 

 this coagulative change. But in the experiments cited above in 

 this paper eggs that have first cleavage spindles (cf. many eggs 

 normally fertilized during maturation phases) respond to insemi- 

 nation. Such eggs will develop without the cortical changes that 

 in normal eggs follow insemination. We should, however, point 

 out that, according to Heilbrunn, hypertonic sea-water coagulates 

 the egg. 1 It may thus be argued that those eggs with spindles are 

 only incompletely activated if they give cortical response to insemi- 

 nation. The truth, though, is quite otherwise. The cortical 



i All that Heilbrunn shows is that the eggs are more viscous while in hyper- 

 tonic solutions. We are told nothing of their history after return to normal 

 sea-water. 



