38 
Wager. — The Nucleolus and Nuclear Division 
Macallum 1 shows that the reaction for phosphorus obtained in nuclei 
by means of his nitric-molybdate reagent indicates the presence of chromatin 
in the nucleoli. ‘ The eosinophilous nucleoli in animal and vegetable nuclei 
give a strong reaction for phosphorus, but less marked than in the case 
of chromatin. On the other hand, the nucleolar elements in the nucleus 
of the ovary of Erythronium which are rich in “ masked ” iron, give a deep 
reaction for phosphorus. A similar result was obtained in the nucleoli of 
the nuclei of the embryo-sac of the same form, in the peripheral nucleoli of 
the maturing ovarian ova of Menobranchus , in the nucleoli of Corallorhiza 
multiflora and of Spirogyra, all rich also in “masked’' iron.’ 
A very interesting case, on the animal side, in which the nucleolus 
takes part in the chromosome-formation is that of Actinosphaerium. Here, 
according to Hertwig 2 , the nucleolus, at one stage in the life-history of the 
organism, consists of plastin only (plastin-nucleolus) ; at another stage both 
plastin and chromatin are collected into a single homogeneous body, the 
plastin-chromatin-nucleolus. There is, however, no sharp distinction be- 
tween them, the one passing gradually into the other so that the more 
chromatin the nucleolus contains the more it reacts like the chromatin- 
nucleolus, and vice versa. In mitosis the plastin-chromatin-nucleoli produce 
fine ramifying threads, which exhibit a granular appearance. The granules 
react like chromatin, whilst the ground-substance reacts as plastin. The 
equatorial plate is formed out of these threads. In the division of the 
primary cysts, which result in the formation of secondary cysts (gametes), 
the daughter-nuclei are reconstituted in such a manner that the chromatin 
remains distributed on the nuclear network, whilst the nucleolus is com- 
posed of plastin. In mitosis the chromosomes are formed out of the 
nuclear thread. As they become grouped to form the equatorial plate, the 
plastin-nucleoli become drawn out into fine granular filaments, which sur- 
round the chromosomes and become more or less incorporated with them. 
The spindle is formed out of the nuclear network and cytoplasm, but the 
connecting fibres between the two groups of daughter-chromosomes appear 
to be formed out of the plastin-substance of the nucleolus. The rudiments 
of the plastin-nucleoli appear as blisters in the chromatin masses, from 
which Hertwig suggests the possibility that both plastin and chromatin are 
modifications of, or represent the same element in, the nucleus. 
According to Nemec 3 , the nucleoli consist of a substance like plastin. 
The development of the spindle coincides with the disappearance of the 
1 On the Detection and Localization of Phosphorus in Animal and Vegetable Tissues, Proc. 
R. Soc., lxiii, 1898. 
2 Ueber Kerntheilung, Richtungskorperbildung und Befruchtung von Actinosphaerium Eichhorni . 
Abh. bayer. Akad. d. Wiss., 1898. Ueber die Bedeutung der Nucleolen, Sitzungsber. Bot. Ges. 
Munchen, xiv, 1898. See L’Ann^e Biologique, iv, 1898. 
3 Cytologicka pozorovani na vegetacnich vrcholech rostlin : Vestnik krai. Cesk^ spolecnosti 
nauk Prag, xxiii, 1897 (see L’Annee Biologique, iv, 1898) ; Zur Physiologie der Kern- und 
Zelltheilung, Separatabdruck aus Bot. Cent., lxxvii, 1899. 
