274 EARLY ECHINODERM DEVELOPMENT 



discussion of mitochondrial basophila attributed to perimitochon- 

 drial aggregation of microsomes). This may be connected with 

 the fact that these particles contain proportionately much less 

 ribonucleic acid than microsomes (Schneider and Hogeboom, 

 1950), at least in adult mammalian cells, but it may also be due 

 to the lipid sheath which surrounds a mitochondrion. 



Shaver (1955) undertook an examination of the question of 

 mitochondrial gradients in sea urchin embryos of two species, 

 Lytechinus pictus and Strongylocentrotiis purpuratiis. The tech- 

 nique described by Gustafson and Lenicque ( 1952 ) was followed 

 as closely as possible, and other methods recommended for the 

 visualization of mitochondria were also used. The most satisfac- 

 tory fixatives employed were Altman's fluid or 1 % osmium tetrox- 

 ide; the stain which yielded best results was fast green and safra- 

 nin. All preparations were of embryos fixed and flattened on 

 coverslips. Concurrent studies were also made with the phase 

 contrast microscope of both intact embryos and of homogenates. 



Details of the results cannot be given here, but certain points 

 relating to the question of mitochondrial gradients may be noted. 



1. The method employed by Gustafson and Lenicque (1952) 

 for the identification of mitochondria appears to be unsatisfactory. 

 The technique used by these investigators consists of vitally 

 staining embryos with Nile blue sulfate, flattening them under 

 coverslips, and counting particles (as mitochondria) within an 

 area marked off by a reticule oriented ( in mesenchyme blastulae 

 or later stages) along the animal-vegetal axis. 



Some preliminary observations by Shaver of eggs stratified at 

 10,000 g and stained with Nile blue sulfate indicated that the dye 

 is absorbed by most of the particulate elements of the cytoplasm, 

 by some of the elements of interphase nuclei, and, to a lesser de- 

 gree, by the hyaloplasm. In intact cells, it appeared very uncer- 

 tain which elements were mitochondrial on the basis of coloring 

 by Nile blue sulfate. 



2. Mitochondria in various types of cells have been described 

 as being of different sizes. The usual range given for these parti- 

 cles from adult tissue cells is from 0.5-2.0 microns in diameter, 

 and up to 7.0 microns in length. Observations of mitochondria 



