90 



GENERAL PHYSIOLOGY 



characterised by lively activity, in which the principle of surface- 

 enlargement by branching is especially expressed. 



b. The Substance of the Nucleus 



As regards the nature of the substance of the nucleus, exactly the 

 same is true as in the case of the protoplasm. The nucleus is no 

 more a unitary substance than is the protoplasm. It is a morpho- 

 logical structure, an organoid of the cell, which consists of several 



FIG. 31. Cells containing different forms of nuclei, o, Vorticella, a ciliate infusorian, possessing a 

 rod-shaped nucleus, b, Stentor, a ciliate 'infusorian, possessing a moniliform nucleus, c, c, Cells 

 of the spinning-glands of the caterpillar possessing antler-like branched nuclei. (After 

 Korschelt.) 



different constituents that may be distinguished from one another 

 microscopically more or less clearly, and all of which are not 

 present in all cells at all times. Because of the exceeding minute- 

 ness of the objects, it is often difficult sharply to characterise the 

 individual constituents. Therefore, their identity in two separate 

 species is not always beyond doubt, and extended investigations 

 are still needed before it will be known clearly what constituents. 



