88 MARY ELMORE SAUER AND DONALD DUNCAN 



bodies. Those which are dish-shaped, lens-shaped, broken ring-shaped, and 

 possibly also those consisting of several granules, are features of the neuro- 

 epithelial layer during the period of highest mitotic activity (8 to 15 hours 

 after 200 r) when numerous cells break down in division. This period is 

 approximately coextensive with the first mitotic period following irradiation. 

 Since these bodies occur at all depths of the neuroepithelial layer, while 

 dead cells are chiefly observed adjacent to the lumen, the bodies must have 

 been moved into the depths of the wall following cell death. Although some 

 are cast into the central canal, it may be speculated that others are resorbed 

 at the lumen into the cytoplasm of adjacent nuclei which are beginning 

 their postmitotic migration peripherally (Sauer, 1935; Sauer and Chitten- 

 den, 1959; Sauer and Walker, 1959: Sidman et al, 1959; Watterson et al, 

 1956). Evidence for the actual process of phagocytosis is completely lacking 

 in sectioned material; however, to one who has marveled at the antics of 

 cells in tissue cultures, as demonstrated with time-lapse photography, rapid 

 absorption of degenerated cell remnants seems plausible. The many chro- 

 matin bodies surrounded by only intact cells can be explained readily in 

 this way. 



In addition to the irregular bodies which seem to be degenerated mitotic 

 cells, after irradiation there are also larger, Feulgen-positive bodies more 

 nearly approaching a cell nucleus in size. After 500 r these are the first 

 bodies to appear in the neuroepithelial layer. They begin about the time 

 of resumption of mitosis and become numerous 4 to 5 hours following irra- 

 diation (Fig. 9) . The picture is clean-cut, in contrast to the same region seen 

 overlain with small fragments at 10-14 hours following 200 r. Similar large, 

 spherical bodies occur in enormous numbers in the mantle layer of our older 

 irradiated chick embryos and of irradiated Chinese hamster embryos of com- 

 parable age. Their large sizes suggests whole pyknotic nuclei. It is assumed 

 that they are differentiating cells which have died a pyknotic type of death 

 in interphase. Since they begin to appear even in the period of mitotic arrest, 

 they are unrelated to mitosis. (Hicks, 1958 and Hicks et al., 1959) has studied 

 this radiosensitive form extensively. Some in the neuroepithelial layer are 

 definitely cytoplasmic. In the mantle layer, few intact cells remain. 



Those Feulgen-positive bodies definitely enclosed in mitotic stages at the 

 lumen are considered to be micronuclei. In some material they are rather 

 numerous. As the nuclei of these mitotic cells migrate into the depths of the 

 wall in their postmitotic period, their micronuclei will be drawn with them. 

 Consequently, some of the mitotic bodies deep in the wall must also be 

 micronuclei. 



How many of the numerous, spherical bodies, about 2 /x in diameter and 

 apparently cytoplasmic, are actually micronuclei is unknown. That some 

 may represent a direct extrusion from the nucleus is a possibility. This might 



