STUDIES IN THE LIFE-HISTORY OF EUGLENA. 339 



According to this system of classification, the nucleus of 

 Euglena agilis is of type three, yet the fact of the apparent 

 karyokinetic division would indicate a modification of the type. 



Various descriptions have been given of the Euglenoid nucleus: 

 Biitschli (1889), Steuer (1904), Haase (1910), Hamburger (1911), 

 Tschenzoff (1916), Hall (1923), considered it similar to the nuclei 

 of other plant and animal cells so far as the chromatin material 

 was concerned. Klebs (1883), Dangeard (1902), Dehorne 

 following Dangeard (1920), record a spireme structure in the 

 resting nucleus. It is quite probable that the latter descriptions 

 are of nuclei in the early prophase stages of division rather than 

 in the resting condition. 



Keuten (1895), described well formed chromosomes in the 

 resting nucleus of Euglena viridis, but here again it seems probable 

 that prophase stages were observed. 



The description as given by Tschenzoff (1916), seems to be 

 typical for many of the Euglenoid nuclei, that of Euglena agilis 

 included. He described a central " Binnenkorper " around which 

 is found " chromatische substanz in Form von feinsten Brockchen 

 und Fadchen. Manchmal tritt mehr brockliche Beschaffenheit 

 des Chromatin, manchmals feinfadige Zutage. Manchmal die 

 Chromatin konnen auf einer Netwerk aufgereiht zu sein, . . . 

 Ein geschlossenes Webenwerk konnte ich nicht festellen, wenn 

 auch das Vorhandsein eines solches zu vermuten ist." 



This description agrees with that of Butschli (1883-1889) for 

 nuclei of Euglenoidina in general and with the descriptions by 

 many other observers. It might well be added that in several 

 species of Euglena examined the endosome is fragmented, the 

 fragments often being indistinguishable from the granules of 

 chromatin when stained with haematoxylin . 



On the whole, there seems to be no single distinct type of 

 nucleus characteristic of the Euglenidse. We must face the fact 

 therefore, that much more detailed work needs to be done on the 

 group before an accurate classification of the nuclei can be made. 



The Endosome. 



This structure has led to much discussion among various 

 observers as to both structure and function. It was first defined 



