No. 3.] THE PROTOZOA AND METAZOA. 749 



The exact history of the achromatic body of Spirochona 

 is not given either by Hertwig or Balbiani. The former says 

 that at times of division the homogeneous part enlarges, and a 

 small central granule, which he calls the "nucleolus," appears. 

 This gradually changes by sending out amoeboid processes, 

 after which it becomes more and more indistinct until it can 

 no longer be made out. The granular chromatic portion breaks 

 into smaller pieces until the entire nucleus appears homogene- 

 ous. After this two masses of homogeneous substance, which 

 he calls the " end plates," appear at the two extremities, and 

 these he regards as the same substance as the original homo- 

 geneous portion. Balbiani also thinks that the " end plates " 

 or pole-plates (Calottes) are the same as the homogeneous part 

 of the resting-nucleus.^ 



In all the larger Spirochona nuclei the homogeneous part 

 {i.e., the "achromatic body") encloses that granule which 

 Balbiani with Hertwig calls the " nucleolus." In smaller 

 nuclei, on the other hand, an analogous body is found in the 

 granular and not in the homogeneous part. Hertwig shows 

 no connection between these two granules, but claims that the 

 " nucleolus of the homogeneous part is the homologue of the 

 metazoan nucleolus." Plate ('86) gives a somewhat different 

 account, and admits a possible identity of the two. The 

 "nucleolus" of the homogeneous part, he thinks, is formed 

 from particles of chromatin which penetrate, while in solution, 

 from the granular into the homogeneous portion, and there 

 reform into the solid refringent corpuscle. Biitschli regards 

 the corpuscle as a condensation of the chromatin-reticulum of 



comme la partie granuleuse, mais les filaments sont plus courts, plus fins, beau- 

 coup moins nombreux, et au lieu d'etre places parallelment les uns aux autres, ils 

 s'entrecroissent diversement dans la substance homogene et transparente (sue 

 nucleaire) dans laquelle ils sont plonges. De plus ils ne se colorent pas, ou fai- 

 blement, par les colorants de la chromatine, notamment le vert de methyle, et se 

 montrent des lors comme formes d'achromatine. Cette structure de la partie 

 homogene ne s'observe que dans les noyaux qui ne contiennent pas encore un 

 nucleole (centrosome) ou dans ceux ou le nucleole se trouve encore dans la partie 

 granuleuse, lorsqu'il est parvenu dans la partie homogfene les filaments achroma- 

 tiques prennent une autre disposition que nous decriron par la suite " (p. 24S). 



1 " Nous pouvons done conclurer i une identite morphologique et chimique com- 

 plete entre les masses polaires du noyau en division et la partie achromatique du 

 noyau au repos " (p. 292). 



