■462 University of California Publications in Zoology [Vol. 20 



The Resting Nucleus 



Tschenzoff (1916) describes the resting nucleus of Euglena viridis 

 as containing a " Binnenkdrper" around which is found the 



chromatische Substanz in Form von feinsten Brockchen und Fadchen. Manchmal 

 tritt mehr brockliche Besehaffenheit des Chromatins, manchmals feinfadige zutage. 

 Manchmal die Chromatinkornen auf einer Netwerk aufgereiht zu sein. . . . Ein 

 gesehlossenes Webenwerk konnte ieh nicht feststellen, wenn auch das Vorhandsein 

 eines seiches zu vermuten ist. 



His description agrees with that of Belaf (1916) for Astasia, Hart- 

 mann and Chagas (1910) for Peranetna, Steuer (1904) for Eutreptia, 

 and Biitschli (1883-1889) for euglenoids in general. Klebs (1883) 

 seems to have mistaken a nucleus in the early prophase for the typical 

 resting nucleus, since he describes a spireme structure in the nucleus 

 of Euglena. Keuten (1895) has also described a prophase, since he 

 mentions distinct chromosomes in the resting nucleus of Euglena. 

 Dangeard (1902) considers the nucleus of Euglena and other 

 euglenoids to contain a karyosome, around which is wound a long 

 chromatin thread, the coils of which present the appearance of 

 chromosomes. This concept of the euglenoid nucleus has recently 

 been revived by Dehorne (1920) in his work on Euglena. 



The structure of the nucleus in Menoidium is similar to that 

 described for Euglena by Tschenzoff. In Menoidium, however, the 

 nuclear membrane appears to persist throughout mitosis, while 

 Tschenzoff states that in Euglena 



eine eehte doppelkonturierte Membran ist indessen auscheinend nicht voihanden, 

 sie wird nur manchmal durch ein Kunstprodukt vorgetauscht. Wahrend des ganzen 

 Prozesses der Kernteilung wird sie regelmassig vermisst. 



Yet in his figures the outline of the nucleus stands out sharply from 

 the cytoplasm, so that a membrane of some sort may well nave been 

 present. Dehorne (1920) finds a nuclear membrane persisting in rare 

 cases only. Dobell (1908) describes the nucleus of Copromonas as 

 bounded by a nuclear membrane and containing a karyosome, around 

 M'hich there is a clear zone containing "achromatic granules" and 

 crossed by radial "linin threads"; his "achromatic granules" evi- 

 dently correspond to the chromatin granviles which give rise to the 

 chromosomes in the mitosis of other euglenoids. 



