292 BULLETIN OF THE 



dare to assert that this mode does not exist among animals. Even in 

 the case where the nucleus disappears, however, it in all probability- 

 forms none the less the central part of the molecular stars ; and as it is 

 in the centre of these stars that the new nuclei reappear, it may be pre- 

 sumed that the latter are, at least in part, composed of the very sub- 

 stance which constituted the nucleus before its division. 



It is the origin of the new nuclei at the centre of the asters which is j 

 most strikingly in contrast with the results obtained in studying Limax. 

 Fol also failed to recognize the fact that the deflected rays, which com- 

 pose what is now known as the spindle, were in any essential respect 

 peculiar. This oversight may have had its influence in preventing the 

 author from giving an accurate account of the method in which the new 

 nuclei arise. 



The ''line" of coarser granules may have been the first trace of the 

 forming " Kernplatte," although no connection with the bent rays that 

 pass from pole to pole of the spindle was indicated by the observer. 

 Compare Fol's Fig. 5, Plate VIIL, with Fig. 82 of Limax. 



In another point there is considerable divergence between Fol's ac- 

 count and my own observations. In Limax the asters can be made vis- 

 ible by the use of acetic acid much earlier than is represented in the 

 case of Pteropods. Might they not have been demonstrated by Fol 

 for a somewhat earlier stage (e. g. for that shown in Fig. 2, PL VII.) 

 by a more careful or prompt employment of acetic acid 1 If not, then 

 we have to do in these cases with heterochronic variations. The com- 

 parison may be taken to aff'ord ontogenetic evidence of a palingenetic con- 

 centration of the events of nuclear metamorphosis in the case of Limax. 

 What the immediate motive to such an acceleration may have been, it is 

 not easy to conjecture. 



Strasburger ('75). The reader is referred to p. 372 for a synopsis 

 of the results of Strasburger's studies, as the first edition of his work has 

 not been accessible. 



The first of a series of valuable articles by 0. Hertwig ('75) embraces 

 the results of observations made chiefly on Toxopneustes lividus. The 

 results obtained by the use of hardening reagents were controlled, as far 

 as possible, by studies of the living egg. Around the nucleus of the first 

 segmentation sphere (Furchungskern)the protoplasm has a radial arrange- 

 ment which stretches to the periphery of the yolk, and in the immediate 

 vicinity of the nucleus there gradually collects a homogeneous substance 

 destitute of granules ; furthermore, the nucleus itself undergoes a slight 

 change of form, which is interpreted as the result of its amoeboid motion. 



