366 MARGARET R. LEWIS AND WARREN H. LEWIS 



A study of the fixed specimens seems to show that the mito- 

 chondria retain somewhat their original character and shape 

 dm'ing mitosis (figs. 14-17). They are, however, almost always 

 shorter and more scattered through the cytoplasm than in the 

 surrounding cells (figs. 4, 5, 14 a, 15 b, d, 17, 18). There are 

 usually as many and often more mitochondria in the early stages 

 of the dividing cell than in the neighboring cells (figs. 4, 5, 

 14 a, b, 15 b). 



There is no indication in the fixed specimens of any arrange- 

 ment of the mitochondria about the spindle in such a manner 

 that they would undergo division into two parts in the plane 

 of cleavage of the dividing cell. On the other hand, all of our 

 specmiens seem to show that the mitochondria tend to become 

 more evenly scattered through the cytoplasm during division, 

 and those that happen to be on either side of the cleavage plane 

 are carried into the respective daughter cells. 



Since each daughter cell contains only about one-half the 

 number of mitochondria found in the mother cell at the time of 

 division we must assume that there is an increase sometime 

 during the life of the cell between one division and the next, 

 otherwise the number would rapidly decrease during each suc- 

 cessive division. Now the question is: When does this increase 

 take place? Is it during the so-called resting period, or during 

 mitosis? In some of the fixed preparations where mitotic figures, 

 daughter cells and young growing cells are numerous, it is possi- 

 ble to arrange cells in a series according to the stage of recon- 



Fig. 15 Arrangement of mitochondria during metaphase; a, b, c, f, cells from 

 2-day cultures of heart from 5-day chick embryos; d, e, cells from a 3-day culture 

 of intestine from an 8-day chick embryo; X 540 diam. 



Fig. 16 Arrangement of mitochondria during anaphase and telephase and 

 young daughter cells, a, b, c, from a 3-day culture of intestine from an 8-day 

 chick; X 540 diam. Cell a, anaphase has 156 mitochondria, the two daughter 

 cells, b, have 12? and 125 each, while the older daughter cell, c, has 151 mito- 

 chondria; the neighboring adult cells in this region have been 70 to 160 mito- 

 chondria; d, 3-day culture of intestine from a 7-day chick; the two daughter cells 

 with the smaller dark nuclei have 92 and 49 mitochondria, while the adjoining 

 resting cells have only 77 and 48 mitochondria each; X 790; e, daughter cell from 

 a 2-day culture of heart from a 5-day chick, with very different type of mitochon- 

 dria; X 540 diam.; osmic acid vapor and iron hematoxylin. 



