1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 249 



Chatton (1910) attached much importance to the absence, per- 

 sistence, or disappearance of the nuclear membrane. Alexeieff 

 (1913, p. 357) said, "Je ne puis pas portager 1'opinion que la per- 

 sistance ou la disparition de la membrane nucleaire a quelque im- 

 portance." After citing C entropy xis aculeata, Octomitus intestinalis, 

 where the nuclear membrane persists through all phases of mitosis, 

 and Hexamitus intestinalis in which the nuclear membrane disappears, 

 Alexeieff (1908) concluded: "En effet dans beaucoup de cas il est tres 

 malaise de decider si la membrane nucleaire a disparu complement, 

 ou si elle est seulement amincie; souvent il n'y a q'une separation 

 physique entre le cytoplasme et le sue nucleaire (comme entre deux 

 liquides immiscibles) et 1 'image cytologique peut etre dans ce cas 

 difficile a interpreter." 



Calkins in 1898 and in later works describes Tetramitus chilomonas 

 as an example of a non-nucleated flagellate or rather of a distributed 

 nucleus. He likewise (1899) considered Chilomonos paramoecium to 

 have no nuclear membrane. Kepner and Edwards (1916) prove 

 this latter to be incorrect. I came to the same conclusion from 

 observations of material put up in 1916. I am, therefore, skeptical 

 of the accuracy of Calkin's description of Tetramitus chilomonas. 

 This form, so far as I can judge, is not a true Tetramitus but of a 

 typical Chilomonas structure. The granules of the cell may or may 

 not be chromidia. Distributed granules of some character (idio- 

 chromatin or paramylum) are characteristic of the genus Chilomonas, 

 The division center would thus be considered either within the nucleus 

 or the karyosome. It needs correction, verification, or elucidation. 



The nature of the division center in flagellates is not well under- 

 stood. Prowazek (1903) classifies flagellates with regard to this division 

 center and his work was accepted with slight additions by Dobell 

 (1908). Chatton (1910) classified primitive mitoses in Amoeba, basing 

 his system upon the relationship of the division center to the nucleus 

 and karyosome. Alexeieff (1913) gave a most elaborate system of the 

 primitive mitoses, so elaborate, in fact, that it is of little service. Most 

 references in recent years have reverted to the simpler system of 

 Chatton (1910). In all of these the relationship of the division center 

 to the nuclear chromatin has been accepted as the basis of differen- 

 tiation. Calkins (1903) based his system upon the behavior of the 

 chromatin. He (1899), however, based his conception of the evolution 

 of metazoan mitoses upon the extranuclear division center of Noctiluca. 



