248 Causes and Course of Organic Evolution 



advance is sho-^Ti. For liere, in addition to the above details, 

 there gradually appear in the protoplasm, and often rather 

 diffusely scattered through it, minute spots of nucleo-protein 

 or chromatin substance, that give the characteristic chromatin 

 reactions. These seem often to be isolated, but e\ddently 

 in some cases, and probably in all cases, they are linked to- 

 gether by fine connecting viscous threads (p. 52). In the 

 higher Blue-green Algae specially (Oscillatoria, Lyngbija, Rivu- 

 laria, etc.), these form a very definite skein or loose thread-coil 

 on which chromatin granules are disposed. It becomes im- 

 portant then to know how these behave during division. While 

 Hansgirg and Fischer have doubted the existence of, and 

 formation of, phases in chromatin division of a rudimentary 

 cell nucleus, Hegler, Wager, Olive, and Phillips have all traced 

 division changes of a fairly definite nature. These consisted 

 in aggregation and rearrangement of the previously diffuse 

 chromatin masses, in a splitting of the constituent aggregation 

 material into halves that retreated towards the poles of the 

 cell, in the presence of connecting threads that temporarily 

 united these, and in gradual rearrangement of the whole to 

 form conditions typical of the resting cell. But careful and 

 extensive study of the unicellular genera, and even renewed 

 observation of different thread-forms such as the Rivulariese, 

 must be made before final conclusions can be reached. 



The decided trend of evidence however is strongly in favor 

 of the view that a loose or open chromatin nucleus exists 

 in the higher Cy anophy cese ; that this is devoid of a nuclear 

 membrane, and has not yet aggregated centrally to form a 

 nucleus; that, from behavior of the chromatin previous to 

 division of each cell, it is becoming an initiative and directive 

 substance that stimulates and guides the protoplasm during 

 division; while from its staining reactions and behavior, in 

 comparison with higher i)lants, it seems to be composed of 

 like substance with the chromatin of the latter, and so in all 

 probability is becoming the main hereditary center of each 

 cell. But one important fact deserves to be emphasized. 

 It is that in the simplest Acaryophyta, where no chromatin 



