322 GEACE MEDES 



in freie Siiure unci Metall gespalten und letzteres vielleicht an 

 das lebende Protoplasma gebiinden, wiihrend die Saure selbst 

 frei bleibe." The action of the salt will then be specifically 

 that of the metal in those instances where the acid itself is not 

 harmful or where some other substance is present which neu- 

 tralizes the effect of its anions. 



In his succeeding series of articles he deals with three main 

 problems: ('97) what inorganic substances are indispensible in 

 the medium for the normal development of the Sea-urchin; 

 ('01) what role does each of these substances perform; and finally 

 ('03), are the chemical processes which accompany embryonic 

 development immovably fixed, or does the developing organism 

 possess the power to regulate its chemical composition, even in a 

 varying medium so that the normal end product will be obtained. 



In these investigations he confirms the conclusions arrived at 

 previously, that each substance in the medium produces its 

 specific effect and that the various elements normally present 

 in the sea-water may, in only a few instances and to a limited 

 degree, be replaced by closely allied substances. Throughout 

 his discussions he emphasizes repeatedly the fact that the 

 effects vary in intensity on the individuals derived from the eggs 

 and sperms of different parentage and even on those of the same 

 parentage. Moreover, he shows that eggs obtained in different 

 years and seasons in some instances respond differently to the 

 same treatment. Temperature also plays an important role in 

 producing modifications. 



Fischel ('09), on account of the important role played by 

 the chlorides of potassium, magnesium and calcium in regu- 

 lating the oxidation processes in artificial parthenogenesis of 

 sea-urchin eggs, investigated the action of these salts upon nor- 

 mally fertilized eggs in order to determine their specific effect in 

 ]3arthenogenesis, and to obtain more detailed knowledge of 

 fertilization itself. He replaced part of the sea-water with iso- 

 or hyper-tonic solutions of the above mentioned salts and con- 

 cluded that the injuries produced resulted from chemical modifi- 

 cations of the protoplasm. Longer exposure to these altered 

 conditions or briefer subjection to stronger solutions, involved 



