LIVING SUBSTANCE 



89 



trast to the protoplasm by its characteristic behaviour toward 

 certain reagents, especially colouring-matters. Nuclear masses 

 possessing these characteristics are the most wide-spread in the 

 organic world. The nuclei of a majority of free-living and most 

 tissue-forming cells among animals and plants are of this type. 

 In it the relation of the volume of the nucleus to that of the 

 protoplasm varies greatly. There are cells in which a relatively 

 small nucleus is surrounded by a large mass of protoplasm, as, e.g., 

 many Foraminifera, while in other cells, the mass of the protoplasm, 

 in comparison with the nucleus, is extremely small, as in most 

 spermatozoa. From the type of the single, more or less spherical 

 nucleus deviations in very different directions occur. First, as 

 regards the number of nuclei: 

 As has already been seen, 

 there are organisms that con- 

 sist of a unitary protoplasmic 

 mass in which lie embedded a 

 large number of nuclei, such 

 as multinucleate cells and 

 syncytia. In such cases the 

 number of the nuclei can be 

 so great and their size so ex- 

 cessively small that, as Gruber 

 ('88) has observed in certain 

 Rhizopoda from the harbour of 

 Genoa, especially Pelomyxa pal- 

 lida, the nuclei lie distributed 

 through the whole protoplasm 

 as a fine powder (Fig. 30). 

 With such a division of the 

 nuclear mass as is present in 

 multinucleate forms, the nu- 

 clear surface naturally is con- 

 siderably larger than with the 

 same quantity contained in a 



single large nucleus a fact that is particularly important from 

 the physiological point of view. 



The same principle of surface-enlargement is seen also in the 

 differentiation of the form of the single nucleus. The most mani- 

 fold and extreme deviations from the typical spherical form occur. 

 Rod-shaped, band-shaped (Fig. 31, a,) and moniliform (Fig. 31, &) 

 nuclei are very common among ciliate Infusoria.. Going still fur- 

 ther, the same principle leads to star-shaped and branched nuclei, 

 which are found in certain cells in the bodies of insects, and reach 

 their highest development in antler-like branched forms in the 

 cells of the spinning-glands of many caterpillars (Fig. 31, c). It 

 seems noteworthy that it is the nuclei of secreting cells, i.e., cells 



FIG. BO. Pelomyxa pallida, a rhizopod-cell from 

 the harbour of Genoa, containing finely- 

 divided nuclear substance in the protoplasm. 

 (After Gruber.) 



