742 CALKINS. [Vol. XV. 



A spireme-stage is wanting in the prophase of Actinosphae- 

 rium, and I have been unable to demonstrate a typical spireme 

 in Noctihcca, although, as previously pointed out, the chro- 

 matin passes through a stage which simulates the metazoan 

 spireme (Figs. 6, 7, and 12). There are, however, certain Pro- 

 tozoa in which a true spireme seems to occur. Karawaiew 

 ('95) describes spireme-formation in the Radiolarian Aulocaiitha 

 scolymantlia. In the resting stage, this nucleus has a large 

 "spongy" nucleolus, consisting of a dense central mass with 

 numerous branches. When preparing for division the " spongy " 

 mass breaks up into threads, until finally the entire chromatin- 

 mass becomes a tightly wound spireme. Sooner or later the 

 spireme-threads undergo a longitudinal division, at the same 

 time becoming granular. Karawaiew saw no nuclear plate, the 

 next stage after the spireme being a late anaphase in which 

 two striped regions were found at the poles. Each stripe con- 

 sisted of a row of chromatin-granules. The account is by no 

 means complete, and it is probable that more careful examina- 

 tion will show a nuclear plate. 



Our acquaintance with the chromatin-changes in the micro- 

 nuclei of ciliates is more satisfactory. The exceedingly dense 

 structure of the micronuclei has led Hertwig and Gruber to 

 class them as " massive nuclei." During division they swell 

 considerably, a change invariably preceded by a spireme-forma- 

 tion (Maupas ('89) and Biitschli ('76) ). The spireme gives rise 

 to granular chromatin-threads which as in Actinospliaerium, 

 become thicker in the central portion, where they are finally 

 divided by transverse division. 



In the great nuclei of Dinoflagellates also, Biitschli ('85) and 

 Lauterborn ('95) have shown that the chromatin-reticulum 

 becomes "increased in size" until a "much-twisted Knauel " 

 results. After this the chromatin becomes arranged in more 

 or less regular parallel fibers which are divided transversely. 

 Zacharias describes for the same form a much more complex 

 process of mitosis, but his results are denied by Lauterborn and 

 others. 



A much more complicated mitosis, including spireme and 

 chromosome-formation, was described by Pfitzner ('86) in the 



