NUCLEAR DIVISION IN PROTOZOA. 215 



the chromatin reservoir is known to break down into minute 

 granules before division, as they do in Noctiluca. This was 

 early made out by Buck ('78) for Arcella, by Gruber, Hertwig, 

 and others for various rhizopods, and is therefore a widely 

 distributed phenomenon among the lower forms. 



This disintegration of the chromatin masses is a significant 

 and suggestive process and may be regarded as universal in 

 cell life. In the majority of cases the granules are secondarily 

 united into chromosomes of more or less definite shape and 

 size for each species. Among the Metazoa, Brauer's ('93) 1 

 description of the granulation of chromatin before spireme for- 

 mation shows, if not identical, a closely analogous process, and 

 the numerous observations, by various zoologists and botanists, 

 of spireme formation and synapsis stages, apparently belong in 

 the same category. Among the Protozoa, Brauer ('94), 2 Hert- 

 wig (98), 3 and Gruber ('93) 4 have each described the granule 

 formation in Actinospharium EicJihornii, Schaudinn ('96) 5 in 

 Actinophrys sol, Schewiakoff ('88) 6 in Euglypha alveolata, Hert- 

 wig, Biitschli, Plate, and Balbiani in Spirochona gemmipara, 

 Schaudinn, Wolters, Labbe, Clarke, and Siedlecki, in various 

 Gregarinida and Coccidiida. Whatever may be the cause of 

 this disintegration, possibly an expression of the "limit of 

 growth " which Spencer postulates in connection with the rela- 

 tionship of surface and mass to growth, it is apparently a sec- 

 ond stage in chromatin changes, the primary stage being the 

 single chromatin reservoir. 



The disintegrated chromatin or granules which represent the 

 second stage in the specialization of chromatin are in reality 

 the preliminary stage in chromosome formation ; for, by their 

 union into new aggregates, the definite bodies known as chro- 

 mosomes are formed. In many Protozoa the granular stage is 

 permanent throughout resting and active phases of the nucleus, 

 neither the aggregation into a chromatin reservoir nor forma- 



1 Arch.f. mikr. Anat., Bd. xlii. 



2 Zeitschr.f. wiss. ZooL, Bd. Iviii. 



3 Abhand. d. K. Bayer. Akad. d. Wiss., Bd. xix. 



4 Zeitschr.f. wiss. Zool., Bd. xxxviii. 



5 Sitz.-Ber. Ak. Wiss. Berlin, 1896. 



6 Morph.,Jahr. 13. 



