taneously in all parts of the egg and do not change their position 

 until the first division-period, which coincides with the first nuclear 

 division. This vital point is passed over by Petrunke witsch without 

 a word of comment and without bringing forward any correspond- 

 ing observations on the living eggs. In point of fact, I figured con- 

 ditions practically identical with all those of Petrunkewitsch's 

 "series", except the remarkable ring-figure shown in his Fig. 19 (e. g. 

 my Figs. 2c, 5a, 3a — c, from life; Figs. 25 — 35 from sections); but 

 continuous observations on the individual living eggs gave strong 

 direct evidence that these do not represent successive stages 

 in the division of a single primary center, but are varying 

 individual conditions, that often appear side by side in 

 the same lot ofeggs at the same time. 



The author's main assumption that the "series" constructed from 

 his sections represents a succession of genetically connected stages is 

 made without presentation of the least evidence of a division of the 

 centrosomes at any period, or even of the asters; for such spindle- 

 connections as are shown in some of the figures [e.g.^ Figs. 16, 19, 20] 

 will not be considered valid evidence of a preceding division by any- 

 one familiar with the common phenomenon of secondary spindle-for- 

 mation between centers originally separate — indeed it was this very 

 difficulty that I found so hard to overcome in endeavoring to establish, 

 in sections of the entire eggs, the division of the cytasters and of the 

 primary nuclear centrosomes — and it is obviously impossible that 

 a closed ring-figure such as that shown in Fig. 19 (stated at p. 43 to 

 be »ofienbar ein unvermeidliches Stadium«) could arise as a whole by 

 persistence of the original spindle-connections; one, at the least, of 

 the connections shown, must have been secondary. 



It is important to note that the so-called "series" of division- 

 stages of Petrunkewitsch occurs at a period when the asters are 

 large and conspicuous, and at the corresponding period in the living 

 eggs of Toxopneustes are very clearly visible. It is therefore in- 

 admissible to suppose that the discrepancy between his results and 

 my own is owing to a failure on my part to observe the division of the 

 asters at a sufficiently early period. I admit that my observations on 

 the entire eggs do not exclude the possibility of a rapid multiplication 

 of the egg-center at a very early period, before the asters have become 

 clearly visible; but this is evidently not the period on which the con- 

 clusions of Petrunkewitsch are based. 



Indirect evidence of importance is given by the time-relations, 

 to which Petrunkewitsch seems to have given little attention, but 

 he given a few significant details. In general, in his experiments 



