752 CALKINS. [Vol. XV. 



In Actinosphaerium the centrosome has been described by 

 only one observer, Brauer ('94), and its presence has been since 

 denied by Hertwig ('96). Here as elsewhere, however, one 

 positive observation by a good authority must bear more weight 

 than a number of negative statements. Both Hertwig and 

 Brauer are agreed that the pole-plates in ActinospJiaerhtm are 

 derived from the intra-nuclear " achromatic " body of the resting 

 nucleus. Brauer describes an accumulation of cytoplasm out- 

 side of the pole-plates which he calls the cytoplasmic "Kegel." 

 The nuclear membrane is never lost at any point, nor is there 

 any apparent connection between the protoplasmic " Kegel " 

 and the inside of the nucleus, for they are separated by the 

 pole-plates which " machen den Eindruck, als wenn es Verdick- 

 ungen der Membran waren, die stets wahrend des ganzen Kern- 

 theilungsprocesses erhalten bleibt" (p. 204). The cytoplasmic 

 accumulation appears only during mitosis. " Ausserhalb des 

 Kernes an seinen Polen beginnt sich schon, wenn die ersten 

 Veranderungen im Kern erkennbar werden, feinkorniges Proto- 

 plasma anzusammeln " (p. 204). In certain cases centrosome 

 and radiations were seen in this mass, and from Brauer's figures 

 of these stages it appears that the pole-plates at this time are 

 either absent (Figs. 44, 46) or else much reduced (Fig. 45). 

 Brauer is inclined to think that the centrosome is within the 

 pole-plate during prophase and metaphase, and that it finds 

 its way thence into the protoplasm during the anaphase. "So 

 scheint mir der Schluss unabweisbar, dass das Centrosom vorher 

 nicht im Protoplasma ausserhalb des Kernes, wie die Figuren 

 es zeigen, gelegen haben kann " (p. 207). 



Thus in Actinospliacrium the substance of the pole-plates, 

 or a part at least, becomes e.xtra-nuclear for a short time. In 

 Paramoeba (Schaudinn, '96) and in Noctiliica it is permanently 

 so. Schaudinn describes it in Paramoeba as follows: " Dicht 

 neben dem Kern liegt stets das bereits zu Anfang erwahnte, 

 stark lichtbrechende, scharf construirte Gebilde. Ich will 

 dasselbe zunachst mit einem ganz indifferenten Namen, etwa 

 als ' Nebenkorper ' bezeichnen. Bei den kleinsten Amoeben 

 ist es kugelig und ungefahr von derselben Grosse wie der 

 Kern." During spore-formation, pari passti with a progressive 



