378 DEVELOPMENT 



changes external and internal are cause and effect. This is 

 merely a restatement of the Law of Inertia. The entry of the 

 spermatozoon alters the balance of free energy between egg and 

 environment. Loeb attempted to bring about the same result 

 by altering the free energy balance between environment and egg. 

 He found that two separate and distinct changes took place after 

 fertilisation, viz., membrane formation and development. These 

 involve totally different physico-chemical reactions. Membrane 

 formation is not followed necessarily by development. 



I. Membrane Formation. 



Loeb found that all those substances or agencies which can 

 bring about haemolysis (Chap. XXI., p. 244) also induce membrane 

 formation. The best agent for this purpose is dilute butyric acid. 

 Immersion of sea-urchins' eggs (unfertilised) in sea-water con- 

 taining about 5 per cent, of 2V/10 butyric acid for two to four 

 minutes brings about typical membrane formation. This mem- 

 brane is tough and is separated from the egg-substance by a layer 

 of more fluid material. 



Examination of the performance of the other cytolytic sub- 

 stances makes manifest the mechanism of the change brought 

 about by their agency, and its similarity to that caused by butyric 

 acid or other fatty acid. The former all lead to the abnormal 

 production of acids in living protoplasm, and these acids pro- 

 duce, as a secondary effect, the physico-chemical change now 

 under consideration. These cytolytic substances are, as we 

 saw in Chap. VIII., just those substances which break emulsions. 

 Egg protoplasm is an emulsion very rich in fat, and it is obvious 

 that the breaking of such an emulsion would lead to the setting 

 free of protein and would probably change the nature of the 

 complex from a water-(and protein)-in-oil type to an oil-in-water- 

 (and protein) type. The protein and lipoids carried to the surface 

 and coming in contact with sea-water would readily be adsorbed 

 and form a membrane (Chap. X.). 



Eggs undergoing artificial parthenogenesis quickly show dis- 

 integrative changes unless means are taken to confine the cytolytic 

 effect to the surface. This is provided for in some cases (e.g. 

 starfish and certain annelids) by the specific nature of the proteins 

 in the cortical layer. The diffusion of the acid causes them to 

 alter in electrical state. They imbibe water, swell up and develop 

 normally. 



