1923] Hall: Binary Fission of Menoidium incurvum 459 



In Menoidium, as stated above, the paradesmose is spun out 

 between the two daughter blepharoplasts. In Trichomonas Kofoid 

 and Swezy (1915fl) describe in mitosis the division of each blepharo- 

 plast into two new structures, a basal granule (blepharoplast proper) 

 and a centrosome ; while the flagella and paradesmose remain attached 

 to basal granules, or blepharoplasts proper, the centrosomes become 

 located outside the nuclear membrane at opposite ends of the spindle 

 and connected to the blepharoplasts by the nuclear rhizoplasts. In 

 such a case as this the original blepharoplasts would be considered 

 centroblepharoplasts (Kofoid and Swezy, 1919«), since they divide 

 to form both centrosomes and blepharoplasts. In other flagellates, 

 such as Giardia (Kofoid and Swezy, 1922) the blepharoplast is 

 connected by a rhizoplast to a centrosome just outside the nuclear 

 membrane; during mitosis in Giardia the paradesmose is drawn out 

 between the two extranuclear centrosomes. Thus there are two types 

 of paradesmoses, differing in location ; in Giardia, the paradesmose 

 connects the centrosomes, whereas in Trichomonas, in which the 

 centrosome originates from the centroblepharoplast in mitosis, the 

 paradesmose remains connected to the two blepharoplasts. It is quite 

 evident that the paradesmoses of Menoidium incurvum and Euglena 

 agilis are homologous with the type found in Trichomonas, in that both 

 of them are drawn out between the two daughter blepharoplasts, 

 rather than with the paradesmose seen in Giardia. The origin of 

 the extranuclffar centrosome from the blepharoplast (centroblepharo- 

 plast) at the beginning of mitosis has not yet been demonstrated in 

 Menoidium, but from the essential similarity in structure to that of 

 Trichomonas it might be expected that the blepharoplast of this 

 flagellate may be shown eventually to be a centroblepharoplast. 



Gullet and Reservoir 



With the progress of mitosis, the gullet and reservoir begin to 

 prepare for fission; the first step is the general widening of both 

 structures (pi. 41, fig. 17). Then, as the flagella move farther apart 

 the reservoir becomes divided into two lateral portions (pi. 41, figs. 16, 

 18, and 19), each of which is to give rise to a new reservoir. At a 

 later stage (pi. 41, figs. 22-25), the median plane of fission has con- 

 stricted the gullet and reservoir into two daughter structures, one 

 in each new flagellate. 



