G. REVERBERI 321 



plants, the chloroplasts are mitochondria that have acquired new 

 functions. 



It is obvious that all these different functions are based on a 

 peculiar enzymatic constitution, from whence possibly derive the 

 different forms of the mitochondria. Electron microscope research 

 shows that the "cristae mitochondriales" are more numerous in 

 the mitochondria that have a high enzymatic content. One of the 

 principal tasks in the future will be to describe where and how 

 the different groups of enzymes are disposed in a mitochondrion. 

 Probably it will be very useful in the future to compare the 

 localization of the enzymes in the mitochondria and the localiza- 

 tion of the genes in the chiomosomes. If the mitochondria are 

 ultimately responsible for the form, the length, and other charac- 

 teristics of a cell, it would be useful to establish what sort of 

 dependence exists between the mitochondria and the genes. 



Of course it is not intended here to compare the importance 

 of chromosomes with that of mitochondria. It would be sufficient 

 to compare only the ways of their reproduction. Mitochondria 

 grow in length, divide transversely, and are spread at random in 

 the originating cells, because they do not possess that very elabo- 

 rate mechanism which is peculiar to the chromosomes, that is, the 

 "achromatic spindle." Apparently the mitochondria do not possess 

 the very complicated chromosomal structure! 



Mitochondria of the Ascidian Egg 



The assumption that the mitochondria are distributed at ran- 

 dom during the mitotic process must be corrected if the cell which 

 divides is a fertilized egg. We shall see, on the contrary, that in 

 some kinds of eggs there is a sort of mechanism, which is rather 

 accurate and which segregates the mitochondria only in certain 

 cells. Probably that segregation is not only quantitative but also 

 qualitative. 



The importance of this fact is very evident from the embryo- 

 logical point of view, as every cell, while possessing a complete 

 set of genes, does not always have at its disposal the enzymes by 

 which, in consequence of the action of the genes, are initiated 



