ITS CHEMICO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 



45 



fine granules, as large masses, as fibrils, as a framework, or in the 

 form of a honeycomb structure. Further, one such structure 

 may develop into another during the various vital phases of the 

 cell's life-history. 



Hence in formulating a definition of the nucleus, its varying 

 form must be quite disregarded ; the difficulty consists in defining 

 the active substances contained in it, similarly as, in defining the 

 cell, the difficulty lies in describing protoplasm. 

 The nucleus consists of a mass of substances, 

 which are peculiar to it, and which, to a cer- 

 tain extent, differ from protoplasm, and may 

 be distinguished from it. On this account, in 

 all definitions of the nucleus, more importance 

 should be attached to the properties of its 

 structural components than is usually the 

 case. 



The following selection of typical examples 

 will serve to show what a multiplicity of 

 forms may be assumed by the internal struc- 

 ture of the resting nucleus. 



It is beyond dispute that the simplest struc- 

 ture disregarding the molecular conditions 

 discussed later is seen in the nuclei of mature 

 sperm-cells. When the sperm-cells, as is the 

 rule, assume a thread-like form, being the one 

 most suitable for boring their way into the 

 egg-cells, the nuclei constitute the anterior 

 ends or heads of the threads. In the Sola- 

 mandra macnlata the head is like a sword, 

 terminating in a sharp point (Fig. 21 k) ; it 

 consists of dense nuclein which, even when 

 most highly magnified, is still homogeneous in 

 appearance. A short cylindrical body, the so- 

 called middle portion (m), which also appears 

 homogeneous, is joined on to the head; this 

 portion reacts like paranuclein. Hence, ap- 

 parently, it must be considered to form part 

 of the nuclear portion of the sperm-thread; 

 this, however, can only be finally proved when 

 its further development has been observed. 



Further, in sperm elements, where the form of the cell has been 



FIQ. 21. Spermato- 

 zoon of Salamandra 

 maculata .- fc head ; m. 

 middle portion ; ef ter- 

 minal portion ; sp apex ; 

 u undulating mem- 

 brane. 



