160 PHYSICAL CHEMISTRY 



Lyon and Shackell (1910 b) observed that Arbacia eggs are 

 more permeable to many dyes after fertilization. E. N. Harvey 

 (1911) observed that strong bases penetrate fertilized sea urchin 

 eggs more easily than unfertilized. He seems to consider the 

 alkali, however, as a permeability increasing agent to which the 

 fertilized egg is the more susceptible. 



The permeability of the frog's egg increases on fertilization 

 (McClendon, 1914 a, 1915 a). These eggs will live and develop 

 in distilled water. If any substances diffuse out of them, there- 

 fore, they may be detected in the water, and the permeability 

 to the contained substances determined. The permeability of 

 the egg to Na, K, Mg, Ca, CI, S0 4 , and C0 3 is doubled by fer- 

 tilization. Unfortunately it was not possible to measure the 

 increase accurately in less than fifteen minutes in order to deter- 

 mine whether the original increase is partially reversed, as is 

 the case with the sea urchin's egg. 



According to Heilbrunn (191 5) all initiation of development 

 involves gelation of the substance of the egg. It is not under- 

 stood how he can distinguish between gelation of the whole and 

 gelation of parts, such as the membrane and the astral rays. It 

 is well known that the astral rays are highly viscous (by centri- 

 fuge experiments) and a resistance of the egg to deformation 

 before the appearance of the astral rays might be due to in- 

 creased viscosity of the membrane. 



The formation or separation of a fertilization membrane 

 around the Echinoderm egg has given rise to much discussion. 

 Heilbrunn says it is due to decreased surface tension. Loeb 

 supposed it due to secretion of an osmotically active substance 

 beneath the membrane. Glaser (1914) claims that the egg 

 shrinks during the process which is further evidence of increase 

 in permeability. An apparently similar process occurs in the 

 frog's egg and Bialaszewicz (1908) has shown that the egg 

 shrinks during the process. 



A rtificial Parthen ogen esis 

 The eggs of some animals develop without the aid of a sperma- 

 tozoon, a process known as parthenogenesis. Parthenogenetic de- 

 velopment may be complete, as in case of the plant lice, or 

 incomplete, as in case of the eggs of hens and silk worms, which 

 if not fertilized, segment but die before development is complete. 



