. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 380 ERIK ZEUTHEN gressively worse later, even though a statistical rhythm persists throughout cleav- age (cj. Zeuthen, 1951; Holter and Zeuthen, 1955). Slightly increased respiratory cycling by the time when asynchrony sets in is therefore indicative of definitely in- creased cycling in the single blastomeres. Further discussing a point raised by Scholander et al., Clafif (1953) expressed doubts about one of Zeuthen's main summary points (1951) which is (p. 66) : "In the segmenting egg the oxygen consumption follows a r
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 380 ERIK ZEUTHEN gressively worse later, even though a statistical rhythm persists throughout cleav- age (cj. Zeuthen, 1951; Holter and Zeuthen, 1955). Slightly increased respiratory cycling by the time when asynchrony sets in is therefore indicative of definitely in- creased cycling in the single blastomeres. Further discussing a point raised by Scholander et al., Clafif (1953) expressed doubts about one of Zeuthen's main summary points (1951) which is (p. 66) : "In the segmenting egg the oxygen consumption follows a rhythm which throughout segmentation correlates with the ; However, he quotes evidence only from 1949 and 1950, not from the paper from which the summary point is taken. This evidence (Zeuthen, 1951; Holter and Zeuthen, 1955) is the following: Mitotic rhythmicity occurring throughout 10 successive cycles was demonstrated in batches from single females of Psammechinus microtuberculatus. It was stated that in- creasing rates of metabolism occurred whenever a considerable majority of the cells were in mitotic stages characterized by having nuclei with nuclear membranes. For single eggs it was stated that asynchrony between divisions progresses from. 0 0/2 FIGURE 7. Unequal distribution of division frequencies in the 1953 Kristineberg material. 16-cell stage on, but a manifest statistical mitotic rhythm persists throughout cleav- age. Scott and Fox (1952), quoted by Claff in support of his views, do not dis- prove the presence of a statistical division rhythm throughout cleavage in batches of Arbacia eggs, and they did not measure respiration. Actually, their findings can very well be interpreted to agree with Zeuthen's data (1951) demonstrating a statis- tical division rhythm. Nevertheless, it is of course true that the degree of synchronization in batches cannot be expected always to be equally good. During the summer 1953 the author had intended to do mass runs on Ps
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