THE BIOLOGY OF THE CELL SURFACE 



Mitochondria are minute spheres, rods or filaments. In 

 the egg of Platy nereis pictured they are rods; while in that 

 of the closely related Nereis they are spheres. In some 

 cells they assume first one then the other form. It has 

 been held that the mitochondria are phospholipins. How- 

 ever, because with the most careful cytological technique 

 yet devised (that invented by Altmann), later workers^ 

 were unable to prove that mitochondria contain fats but, 

 instead, could demonstrate their protein nature, doubt is 

 thrown on the older view. Certainly in those marine eggs 

 which I have studied on this point, the mitochodria do not 

 reveal the specific gravity of fat; for, when the eggs are 

 centrifuged, instead of lying in the zone next to the fat 

 they take the place above the yolk.- 



Chromldia are generally believed to be cytoplasmic 

 granules derived from the nucleus. I may refer again to 

 the egg of Nereis: in it one can observe granules which 

 seem to come out of the nucleus, wander into the cytoplasm 

 and come to lie at the cell-periphery in which position 

 they can not be distinguished from mitochondria. Under 

 various experimental conditions, as after ultra-violet radi- 

 ation or by treatment with hypotonic sea-water, the 

 number of such granules in the vicinity of the nucleus is 

 increased. Often also with such experimental means chro- 

 mosomes are eliminated which degenerate into granules 

 not easily, if at all, distinguishable from chromidia and 

 mitochondria. This degeneration of chromosomes is quite 

 different from the degeneration of chromosomes in abnormal 

 eggs which fail to develop; these latter can never be mis- 

 taken for chromidia or mitochondria because structurally 

 they offer an entirely different aspect. On the basis of 



^ Bensley and Gersh, /QJJ- 



~ Bensley and Gersh are extremely cautious in their conclusions 

 and it may be that even under the conditions of their experiments the 

 lipin-fraction of the mitochondria iras destroved. 



56 



