286 RUTH STOCKING LYNCH 



The nucleus was spherical and clear with a very distinct bound- 

 ary which made it conspicuous under all magnifications. In 

 the isolated cells and in the compressed cells of the interior of the 

 growth membrane the nucleus was usually central, while in the 

 marginal cells it was more proximal, with the greater mass of the 

 cytoplasm lying between it and the free edge of the cell (figs. 3, 

 4, 21, 22, 23). As has been stated, cells with two or more nuclei 

 occurred quite frequently (figs. 6, 12). The nucleolus was usually 

 single and its location varied greatly. In some cases it was even 

 in contact with the nuclear boundary. Sometimes two or more 

 nucleoh were present (figs. 6, 13, 14, 17, 18, 22). The nucleolus 

 of the liver cell was shorter and stouter than that of the en- 

 dothelial cells and often had a granular appearance. 



Mitochondria 



The cytoplasm of the thick compressed cells of the interior of 

 the growth membrane was packed with mitochondria, the out- 

 lines of the individual granules being for the most part indistin- 

 guishable. In the cells at the margin of the growth and in the 

 isolated cells the clear ectoplasm of the processes and of the free 

 cell edge was easily distinguishable and did not appear to contain 

 mitochondria, while the endoplasm was full of them. They were 

 somewhat scattered, especially in the flattest cells (figs. 5, 6, 7, 

 8, 9, 10, 12, 13, 17, 24, 25). They were not constant in shape, 

 size, position or number. In some cells most of the larger 

 mitochondria occurred near the periphery of the endoplasm, but 

 large granules were often found in contact with the nucleus or 

 scattered in the endoplasm. 



The mitochondria varied in length from 1.5 to 4 m- and in width 

 from 0.5 to 1.5 m- In shape they were spherical, oblong, triangu- 

 lar, pear-shaped or entirely irregular. Large blocks sometimes 

 occurred. In some cultures they were quite long and bent 

 (figs. G, 8, 21), but were never thread-like as in the endotheUum. 

 The smallest granules were often arranged Unearly, and when 

 not quite in focus had the appearance of a long knotted thread. 

 The mitochondria usually varied in size and shape in a single cell 

 (fig. 21); but on the other hand, all the mitochondria in a cell, or 



