38 EI SEN. [Vol. XVII. 



of the nuclear membrane, which is fully dissolved before the 

 fiber of the central spindle has reached its immediate vicinity. 



Phylogeny of the Nucleus. — It seems probable that the 

 perfect resting stage of the nucleus, such as is seen in the 

 polymorphous spermatogonia of the testes of Batrachoseps, 

 represents a phylogenetically primitive nucleus, in which the 

 necessity for the formation of chromosomes and chromomeres 

 has not yet made itself felt. In the most primitive nucleus 

 we should expect to find only a limited number of chromioles, 

 which might be readily manipulated by the chromoplast without 

 the assistance of chromomeres and chromosomes. But as the 

 development of the species progressed and more characteristics 

 were accumulated, we may presume that more chromioles were 

 required, perhaps in order to propagate these characteristics. 

 With this increase in the number of chromioles a more compli- 

 cated system of mitosis became necessary ; hence the very com- 

 plicated apparatus of spindles, etc., accompanying the mitosis of 

 all higher cells. In the lowest forms of animal and plant life 

 the chromioles were probably scattered in the cell itself, just as 

 we now find them in the nucleus of Trachelocerca, a flagellate 

 infusorian described by A. Griiber. In this instance there can 

 be little doubt as to the nature of the granules and that they 

 are real chromioles. The granules found in many bacteria 

 resemble also greatly the chromioles of the higher cells ; and it 

 may be possible that in these low organisms the chromioles are 

 only suspended in the cytoplasm, without any surrounding 

 nuclear wall. 



In the blue-green algae, the Cyanophyceae, we have probably 

 a similarly primitive nucleus, in which the chromomeres and 

 the chromosomes have not yet been developed. In a later 

 stage we should expect nuclei with a nuclear wall, but with the 

 chromioles free as in the perfect resting cells in the testes of 

 Batrachoseps. As is well known, many investigators deny the 

 existence of nuclei in the Cyanophyceae and contend that the 

 darker staining substance in the center of the cell is nothing 

 but condensed cytoplasm. But this theory seems to me unten- 

 able in view of the fact that the Cyanophyceae are highly dif- 

 ferentiated plants which certainly would require hereditary 



