J. R. SHAVER 275 



from sea urchin embryonic cells, studied with the phase contrast 

 microscope in homogenates, indicated a size range of from 0.5 to 

 2.5 microns, with a majority of spherical or oval forms being about 

 1.5-2.0 microns in diameter (Shaver, unpublished observations; 

 see Fig. 2a). Electron micrographs of mitochondria in homoge- 

 nates of sea urchin embryos have provided additional information 

 on the size range of these particles in this material (Fig. 2b). 

 Gustafson and Lenicque (1952, 1955) have not given any dimen- 

 sions for the particles identified by them as mitochondria. Agrell 

 ( 1955 ) , however, observing sea urchin embryonic cells under 



Fig. 2. (a) Homogenate of unfertilized eggs, Lytecliinus pictits, show- 

 ing typical forms and sizes of mitochondria. Dark M phase contrast oil 

 immersion objective, 1455 X. (b) Electron micrograph of mitochondrion 

 from homogenate of L. pictiis gastrulae (24 hours; 17° C); dialyzed on col- 

 lodion membrane, fixed with buffered 2% osmium tetroxide; air dried; 

 chrome shadowed. Original magnification, 16,000x. 



conditions similar to those employed by Gustafson and Lenicque 

 ( 1952 ) , states that mitochondria are "dark, round granules, 0.2 

 micron in diameter, very often double granules, or sometimes 

 clustered together in larger aggregates, staining clearly with Janus 

 green." The tendency of small particles in the cytoplasm of cells, 

 vitally stained with Janus green or Nile blue sulfate, to aggregate 

 has also been noticed by Shaver (unpublished observations). It 

 is conceivable that the development of mitochondria from "very 

 small blue units" ( Gustafson and Lenicque, 1952 ) may in part be 

 due to such a phenomenon. 



