METABOLIC CHANGES 327 



Phenomena, which, are still more remarkable, and which indi- 

 cate the part played by the nuclei in the formation of the cell- 

 wall, are to be observed during the healing of wounds in 

 Vaucheria. Numerous small nuclei appear in the protoplasm, 

 which collects round about the wound, thus approaching the 

 upper surface, whilst the grains of chlorophyll are forced back 

 in exactly the opposite direction. By this means the nuclei and 

 chlorophyll grains exchange places. This observation immedi- 

 ately refutes the objection, which might otherwise easily be 

 raised, namely, that the nucleus or nuclei are present in those 

 places to which the protoplasm flows in greater quantities, be- 

 cause they are carried along by the protoplasmic stream. For, if 

 this were the case, we should expect to find the chlorophyll grains 

 also in the same places, since these are much smaller than the 

 nuclei, and may even be induced to change their positions by 

 variations in illumination, which have no effect upon the nuclei. 



" Thus we see," as Haberlandt remarks, " that the nuclei and 

 chlorophyll grains exhibit quite independent changes of position, 

 which, if we assume that they are passive, cannot in any way be 

 influenced by the movements of the granular plasma as a whole. 

 These phenomena that the streaming protoplasm to a certain 

 extent selects the bodies, which it carries along with it, in the one 

 case taking the larger cell-nucleus, and leaving the smaller chro- 

 matophores and neglecting the cell nuclei, which are as small or 

 even much smaller can only be explained by supposing, that 

 their role is to effect definite accumulations, which depend upon 

 the functions of the nuclei and the chromatophores." 



Korschelt (VIII. 8) has demonstrated, that relations, similar to 

 those described by Haberlandt, as existing between the position 

 and the function of the nuclei in plant cells, are also present in 

 animal cells. 



Ova increase considerably in size, by absorbing large quantities 

 of reserve materials. In these, the germinal vesicle is frequently 

 found in that place, where the absorption of material must of 

 necessity take place. Thus, for instance, in one species of Coelen- 

 terates, the ova are derived from the endoderm and are nourished 

 by the gastrovascular system by means of endodermal cells. In 

 conformity with the above-stated law the germinal vesicles of 

 young ova are situated superficially near to the surface of that 

 wall, which is turned towards the gastric cavity (Fig. 164). In 

 many Actinice (Hertwig, VIII. 5b) the ova, for a considerable 



