332 



DEVELOPMENT OF ASCIDIANS 



some observations, that they were "qiiantitativ imgleich verteilt" 

 in the blastomeres. 



Other indications of a differential distribution of mitochondria 

 in some blastomeres of a developing embryo are found in the eggs 

 of Nereis, Eucharis, and probably of Myzostoma (Reverberi and 

 Pitotti, 1940; Pitotti, 1947). In these eggs the Nadi reaction 

 showed definite localization of a certain substance. Confirmation 

 that such a substance is cytochrome oxidase, as we suppose, is 

 however lacking. We hope that coloration of the eggs with Janus 



d e f 



Fig. 8. Nadi reaction (dotted) in developing egg of Bithiinia (Attardo, 

 1955a). 



green will give more information. It is important to note for the 

 moment that, as in the ascidians and in Tiibifex, the Nadi reac- 

 tion is positive only in those blastomeres that will give rise to the 

 larval organs of movement. 



In the "Regulative" Eggs. In the sea urchin egg the topo- 

 graphical distribution of the mitochondria has been studied by 

 Gustafson and Lenicque (1952; 1955). In the unfertilized egg 

 and in the first stages of development there was a small quantity 

 of mitochondria. Their number suddenly increased at the begin- 



