the Echinoderm Egg during Fertilisation. 



225 



place ; and in the absence of these structures the process of cell division makes 

 no further progress, and the chromosomes finally degenerate and break down. 

 This experiment clearly proves that the sperm bring about profound altera- 

 tions in the egg while still external to the egg-membrane. Loeb (8) has shown 

 that when the eggs of Strongylocentrotus are fertilised with the sperm of 

 Asterias, in hyper-alkaline sea- water, they only form fertilisation membranes : 

 no actual segmentation takes place unless the eggs receive further treatment 

 so that artificial parthenogenesis is induced. 



Meyerhof and Warburg in many of their experiments have shown that 

 any injury or cytolysis of the egg-membrane is invariably followed by a great 

 increase in the oxygen consumption of these eggs. Meyerhof (10) found that 

 this is usually accompanied by an increased liberation of heat. In eggs 

 treated with weak solutions of NaCl, in which the normal condition of the cell- 

 wall is destroyed in the absence of Ca and K ions, the rise of oxygen con- 

 sumption was five times that of the same quantity of untreated eggs. The 

 heat production was increased from 09 grm.-calories per hour to 3 - 4 grm.- 

 calories per hour, after treatment with valerianic acid, by which artificial 

 membrane formation had been induced. 



A great many of Loeb's and Warburg's experiments point conclusively to 

 the cortical layer of the egg and the egg-membrane as being the controlling 

 factor in the oxidation processes of the egg. Any change brought about in 

 these is immediately reflected in the oxygen uptake of the egg. Loeb has, of 

 course, based his method of producing artificial parthenogenesis on the fact 

 that alteration of the surface layer of the egg renders the commencement of 

 development possible. But how can the cytolitic destruction of the surface 

 layer of the egg lead to development ? Warburg has shown that there are 

 good reasons for believing that the oxidations taking place in the egg occur 

 mainly at its surface, for NaOH, which does not diffuse into the egg, raises 

 the rate of oxidations more than NH4OH, which readily diffuses into the egg. 

 Moreover, he found (11) that the addition of iron* salts to the broken up eggs, 

 or acetone egg powder, was followed by a considerable increase in the oxygen 

 consumption of these egg preparations. If the iron-content of the egg 

 powder was doubled, the uptake of oxygen was also doubled. He found 

 marked traces of iron in the sea-urchin egg. He suggests that the iron 

 probably acts the part of a catalyser. If the iron were located in the lipoid 

 layer of the egg in a condition in which it was unable to act, some slight 

 alteration in this layer, due to the action of the sperm, might render it active 

 or bring both the iron and the oxidisable substrate into a condition in which 

 they could quickly interact. We know from Thunberg's work (12) that lecithin 

 * Warburg found 0'03 mgrm. iron per gramme dried egg substance. 



