No. 3.] THE PROTOZOA AND METAZOA. 741 



and the daughter-chromatin elements gather around the daughter-nucleoli, 

 witli connecting or " Zwischenfaden " elements, which form parallel lines 

 from pole to pole. These give the striated appearance which is so charac- 

 teristic of protozoan mitosis. The daughter-nucleoli finally become totally 

 separated, and the chromatin, which has become massed at the distal ends 

 of the striae, but which still consists of separate units, forms two clumps 

 around them. 



In these forms the chromatin appears to be perpetually 

 ready for nuclear division, and the many elements never fuse 

 to form a homogeneous chromatin-mass. Brauer ('95) in 

 describing the formation of the chromatin elements carried 

 the analysis a step further in Actinospliacriiivi. 



He found that, as in the metazoan nucleus, the first stage in division is 

 the disappearance of the net knots, the reticulum becoming more distinct. 

 The latter then disintegrates and the nucleus is filled with minute chromatin 

 elements. " Auf einem etwas spateren Stadium ist der ganze Kernraum 

 rait isolirten Kornen, den Chromosomen, erfiillt, deren Zahl nicht zu bestim- 

 men ist " (p. 203). These are not chromosomes, as Brauer states, but 

 elements which fuse later to form the chromosomes extending across the 

 middle of the nucleus. They are ne.\t transversely divided, no longitudinal 

 division taking place. It is probable that such an arrangementof the chro- 

 matin in the nuclear plate of Actinosphaeriuiit represents a primitive stage 

 in chromosome-formation. 



The chromatin in metazoan nuclei passes through a similar 

 stage before each mitosis, and similar elements are welded 

 together to form chromosomes of definite shape and size for 

 each species. A long step in the direction of this metazoan 

 condition is taken by Noctihtca, where chromatin elements are 

 formed as in Actinosphacriitm, but become more compactly 

 fused to form chromosomes of a certain distinct character, and 

 where these chromosomes are divided longitudinally.^ 



1 An entirely opposite view of the significance of chromosomes has been main- 

 tained by Mitrophanow. According to him, the chromatin in the nucleus of 

 Collozoum is a single compact mass ; " la chromatine, en forme d'une petite masse 

 arrondie, et I'achromatine, que a I'aspect de deux appendices coniques" (p. 625). 

 He insists that division here is a simplification of mitosis, which, "deviendra 

 claire, si nous considerons la masse de chromatine comme une chromosome 

 unique " (p. 626). This interpretation stands alone in the literature of protozoan 

 mitosis, and instead of simplifying the problem makes it more complex. Mitro- 

 phanow's material was fixed with nitric acid and stained with an aqueous solution 

 of safranin, and it seems probable, therefore, that a better technique will give quite 

 different results in Collozoum. 



