348 CELL-CHEMISTRY AND CELL-PHYSIOLOGY 



rule is reversed, the nucleus lying near the base of the hair ; but this 

 apparent exception proves the rule, for both Hunter and Haberlandt 

 show that in this case growth of the hair is not apical, but proceeds 

 from the base ! Very interesting is Haberlandt's observation that in 

 the regeneration of fragments of Vaucheria the growing region, where 

 a new membrane is formed, contains no chlorophyll, but numerous 

 nuclei. The general result, based on the study of a large number of 

 cases, is, in Haberlandt's words, that "the nucleus is in most cases 

 placed in the neighbourhood, more or less immediate, of the points at 

 which growth is most active and continues longest." This fact points 

 to the conclusion that " its function is especially connected with the 

 developmental processes of the cell," l and that "in the growth of the 

 cell, more especially in the growth of the cell-wall, the nucleus plays 

 a definite part." 



Korschelt's work deals especially with the correlation between form 

 and position of the nucleus and the nutrition of the cell, and since it 

 bears more directly on chemical than on morphological synthesis, may 

 be only briefly reviewed at this point. His general conclusion is that 

 there is a definite correlation, on the one hand, between the position of 

 the nucleus and the source of food-supply, on the other hand, between 

 the size of the nucleus and the extent of its surface and the elabora- 

 tion of material by the cell. In support of the latter conclusion many 

 cases are brought forward of secreting cells in which the nucleus is of 

 enormous size and has a complex branching form. Such nuclei occur, 

 for example, in the silk-glands of various lepidopterous larvae (Meckel, 

 Zaddach, etc.), which are characterized by an intense secretory activity 

 concentrated into a very short period. Here the nucleus forms a 

 labyrinthine network (Fig. 14, E\ by which its surface is brought to a 

 maximum, pointing to an active exchange of material between nucleus 

 and cytoplasm. The same type of nucleus occurs in the Malpighian 

 tubules of insects (Leydig, R. Hertwig), in the spinning-glands of 

 amphipods (Mayer), and especially in the nutritive cells of the insect 

 ovary already referred to at page 151. Here the developing ovum is 

 accompanied and surrounded by cells, which there is good reason to 

 believe are concerned with the elaboration of food for the egg-cell. 

 In the earwig Forficula each egg is accompanied by a single large 

 nutritive cell (Fig. 163), which has a very large nucleus rich in chro- 

 matin (Korschelt). This cell increases in size as the ovum grows, and 

 its nucleus assumes the complex branching form shown in the figure. 

 In the butterfly Vanessa there is a group of such cells at one pole 

 of the egg, from which the latter is believed to draw its nutriment 

 (Fig. 77). A very interesting case is that of the annelid Ophryotrocha, 

 referred to at page 151. Here, as described by Korschelt, the egg floats 



p. 99. 



