METABOLIC CHANGES 



329 



which is directed towards the ovum, whilst after the chorion has 

 been completed, they retreat into the middle of the cell. 



Still more striking is the behaviour of the nuclei in the so-called 

 double cells, which occur in the eggs of water-bugs (Ranatra and 

 Nepa, Fig. 167 A, B). These develop radiating chitinous pro- 

 cesses on the chorion. The protoplasmic bodies of the two cells, 

 between which a radiation figure develops, coalesce. Daring this 

 process both of the very large nuclei extend numerous fine pro- 

 cesses towards that side, which is turned towards the radiated 

 figure. 



B 



Fig. 166. 



Fig. 167. 



Fig. 166. Egg-follicle of Dytiscus marginalis with neighbouring yolk compartment, in 

 which a large number of granules are being separated off. The germinal vesicle of the 

 ovum is extending processes towards the accumulations of granules. (After Korschelt, 

 PI. I., Fig. 20.) 



Fig. 167. A Transverse section of a secreting double cell from the egg-follicle of Nepa 

 cinereaL. The formation of the radiation figure is s-till taking place ( x 27<> ; after Kors- 

 chelt, PI. V., Fie. 120). B Longitudinal section of a double cell from the egg-follicle of Nepa. 

 Commencement of the development of the radiation figure ( x 195 : after Korschelt, PI. V\, 

 Fig. 121). 



From these and similar observations, Haberlandt and Korschelt 

 draw the following conclusions, respecting the function of the 

 cell-nucleus : - 



1. "The fact that the nucleus is grenerallv found in a definite 

 position in the immature and developing cells, indicates that its 

 function is connected chiefly with the developmental processes of 

 the cell." (Haberlandt.) 



2. "From its position it may be concluded that the nucleus 

 plays a definite part during the growth of the cell, especially 

 during the thickening and increase in superficial growth of the 



