G. REVERBERI 333 



ning of the migration of the mesenchyme cells into the blas- 

 tocoelic cavity. Counts of mitochondria in the early gastrula show 

 that they are more abundant at the animal pole; their number 

 decreases toward the vegetal pole along a gradient. There has 

 been doubt, however, about such mitochrondrial distribution 

 (Shaver, 1955; see also Shaver, this volume). 



In the amphibian eggs and in other regulative eggs no topo- 

 graphical segregation of mitochondria in particular cells of the 

 developing embryo seems to have been described. Of some in- 

 terest is the work of Shaver ( 1953 ) concerning the differentiation 

 or maturation of mitochondria. In fact, while the mitochondria 

 of the young development stages are not able to stimulate a 

 parthenogenetic development, this property is possessed by the 

 mitochondria from late blastula or gastrula. 



Inactivation of Enzymes and Morphogenesis 



In the "Mosaic" Eggs. We have reported above some results 

 which follow the blocking of the cytochrome oxidase or the suc- 

 cinodehydrogenase in ascidian development. Do we have other 

 examples which can confirm such results in the "mosaic" eggs? 

 This can be answered in the affirmative. 



First we want to recall some results obtained by Raven and 

 Spronk (1952) in the Limnaea egg. The topographical distribu- 

 tion of the alkaline phosphatase in the developing embryo of 

 Limnaea has been described by Minganti (1950) who, by his- 

 tochemical methods, showed that it is localized at early stages of 

 development in the stomodaeum, protonephridium, and shell 

 gland. Beryllium is considered a strong inhibitor of the alkaline 

 phosphatase. Raven and Spronk exposed the eggs of Limnaea to 

 beryllium salts. The embryos which developed from these treated 

 eggs showed very marked abnormalities in the stomodaeum, 

 protonephridium, and shell gland. Similar results have been ob- 

 tained by some of my collaborators in this laboratory. 



The research of Lehmann (1941) and Carrano and Palazzo 

 (1955) on the localization of the cytochrome oxidase in the de- 

 veloping eggs of Tiihifex has been mentioned above. The CO. 

 is abundant in the mitochondria, particularly in the 4d cell, that 



