450 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



alkaline, the alkali playing the part of the cytolytic or membrane- 

 forming agent. In the eggs of frogs simple puncture with a fine needle 

 suffices to induce parthenogenetic development, for what reason is not 

 at present clearly understood, although we may fairly infer that it 

 arises from the incidental admixture of certain constituents of the eggs 

 which are normally separated from one another. Artificial partheno- 

 genesis has also been induced in the eggs of plants (Fucus) by treating 

 them with butyric acid, followed by hypertonic sea-water. 



The eggs of all forms which have been made to undergo develop- 

 ment by artificial means yield normal embryos and their development 

 differs in no wise from that of normally fertilized animals. The rearing 

 of marine animals is an excessively laborious task, but Delage has had 

 the courage to undertake it in the case of artificially fertilized sea- 

 urchins and succeeded in maintaining them until sexual maturity. 

 In the case of the frog several specimens arising from artificially 

 fertilized eggs have been brought to sexual maturity by Loeb and 

 Bancroft (see Fig. 28). 



FIG. 28. A parthenogenetic frog. (After Loeb.) 



THE NATURE OF THE AGENTS WHICH FORM FERTILIZATION- 

 MEMBRANES. 



The monobasic acids of the fatty series are all capable of producing, 

 as we have seen, the formation of membranes in the sea-urchin egg 

 provided they are soluble in sea-water. Now this action might con- 

 ceivably be due to the dissociation of Hydrogen Ions by the acids, or 

 it might be due, on the other hand, to the anion or the undissociated 

 molecule of the acid. The latter is the correct alternative, for although 

 the highly dissociated mineral acids will induce Membrane-formation 

 in a limited percentage of eggs, the requisite concentration of these 



