256 THE INDUCTIONS OF BIOLOGY. 



Once more, the so-called nucleus is occasionally a branching 

 structure scarcely to be called a " kernel." 



The facts as thus grouped suggest that the nucleus has 

 arisen in conformity with the law of evolution — that the 

 primitive protoplast, though not homogeneous in the full 

 sense, was homogeneous in the sense of being a uniformly 

 granular protoplasm; and that the protoplasts with diffused 

 nuclei, together with those which are. multi-nucleate, and 

 those which have nuclei of a branching form, represent stages 

 in that process by which the relatively homogeneous proto- 

 -plast passed into the relatively heterogeneous one now almost 

 universal. 



Concerning the structure and composition of the developed 

 nucleus, the primary fact to be named is that, like the sur- 

 rounding granular cytoplasm, it is formed of two distinct 

 elements. It has a groundwork or matrix not differing much 

 from that of the c3'toplasm, and at some periods continuous 

 with it; and immersed in this it has a special matter named 

 chromatin, distinguished from its matrix by becoming dyed 

 more or less deeply when exposed to fit re-agents. During 

 the " resting stage," or period of growth and activity which 

 comes between periods of division, the chromatin is dispersed 

 throughout the ground-substance, either in discrete portions 

 or in such way as to form an irregular network or sponge- 

 work, various in appearance. When the time for fission is 

 approaching this dispersed chromatin begins to gather itself 

 together : reaching its eventual concentration through several 

 stages. By its concentration are produced the chromosomes, 

 constant in number in each species of plant or animal. It 

 is allesred that the substance of the chromosomes is not 

 continuous, but consists of separate elements or granules, 

 which have been named chromomeres; and it is also alleged 

 that, whether in the dispersed or integrated form, each chro- 

 mosome retains its individuality — that the chromomeres 

 composing it, now spreading out into a network and now 

 uniting into a worm-like body, form a group which never 



