No. 3] THE PROTOZOA AND METAZOA. 713 



mostly close to the nucleus. This is the archoplasm or kinetic center of 

 division, and corresponds most probably to the " Nebenkern " df Von la 

 Valette St. George. 



4. In living animals at the stage of (3), the nucleus appears more or less 

 homogeneous and transparent, and is not so distinctly to be seen as the 

 archophisin. But treated with reagents the chromosomes come into view 

 distinctly. 



5. Each chromosome consists of a row of disc-shaped microsomes 

 irregularly scattered in the nucleoplasm. The number of the chromosomes 

 is not clear, but in most cases has been counted to be ten. 



6. The chromatin substance of each of the microsome-discs collects at 

 the periphery and forms a microsome-ring. 



7. In the nucleus of a dividing animal, each microsome-ring splits into 

 half-rings, thus dividing a chromosome in halves, while in that of the spore- 

 forming animals two successive divisions of a microsome-ring take place, 

 so that a single chromosome is directly divided into four daughter ones. 



8. The chromosomes collect on the side of the nucleus which is nearest 

 to the archoplasm and spread out towards the other pole. The pole where 

 the archoplasm lies thus corresponds to Rabl's " Polfeld," and the other 

 pole to his " Gegenpol." 



9. The archoplasm divides and forms a very large spindle which first 

 lies tangential to the surface of the nucleus. This division of the archo- 

 plasm is succeeded by the separation of the chromosomes into two groups, 

 each attracted (?) by its respective archoplasm. 



I o. The archoplasmic spindle thus formed pushes in the nuclear wall on 

 which it lies, and the nucleus assumes in consequence a half-ring form. 



11. By the separation of the archoplasms a spindle is produced which in 

 all essential characters appears like the form known as the " dyaster stage," 

 with a large archoplasmic mass at each end of the spindle. 



1 2. The fibers of this spindle are therefore continuous from one pole to 

 the other, and, lying outside the nuclear wall, become in no way connected 

 with the chromosomes. But there is seen at this stage another set of fibers 

 running from the center of the archoplasm to the polar ends of the chromo- 

 somes. This structure of the spindle corresponds exactly with that of the 

 spermatocyte of Salamandra macnlata, as investigated by Hermann, with 

 only the difference of the persistence of the nuclear wall in Noctiluca, and 

 the necessary modification in consequence of this fact. The optical appear- 

 ance of these two kinds of fibers is different, just as in Salamandra. 



13. Besides these two sets of fibers, the Verbindungsfaden are clearly to 

 be recognized extending between the separating chromosomes. 



14. The central-spindle fibers originate from the archoplasm, the radial 

 fibers, probably from both the cyto- and nucleoplasms, and the Verbin- 

 dungsfaden from the linin substance. 



15. In the spore-buds the archoplasm is to be seen lying close to the 

 nucleus up to the time of full development of the spore, just before its 



