1915] McCulloch: Crithidia leptocoridis 



IV. LONGITUDINAL DIVISION 



In the vegetative phase of the life-cycle the method of reproduc- 

 tion is longitudinal binary fission. A study of the li\ing flagellate.s 

 shows that the first indication of such a process is a slight increase 

 in the width of the elongate forms together with the appearance of 

 two flagella and a subsequent splitting of the protoplasm along the 

 median plane beginning at the anterior end. The stained preparations 

 tend to show that the "kinetonucleus" (pi. 3, fig. 70) divides first. In 

 a few instances there is evidence that the di^-ision of the nucleiLs pre- 

 cedes that of the "kinetonucleus" (pi. 3, fig. 69). Normally the basal 

 granule, flagellum, and "kinetonucleus" divide simultaneously. The 

 splitting of the flagellum proceeds anteriorly while the rhizoplast and 

 axostyle split posteriorly (pi. 3, fig. 69). Along with the above pro- 

 cesses the division of the nucleus to form two daughter nuclei takes 

 place. There is some evidence that at least a promitotic or possibly a 

 mitotic process is present in such a division. As has already been 

 pointed out, plate 3, figures 60 and 62, show three elongate chromatin 

 graniiles. On the same plate, figures 64, 65 and 66, there are spindle- 

 like formations with chromosomic granules not unlike the structures 

 found in the mitotic process of trichomonad flagellates (Kofoid and 

 Swezy, 1915). On the other hand, no centrosome structure has been 

 demonstrated at the poles of the spindle referred to above in plate 3, 

 figures 64, 65 and 66, as found in the trichomonad flagellates. Further 

 investigation may yet reveal such a structure, but since such struc- 

 tures in Crithidia leptocoridis are so small it becomes very difficult to 

 interpret them with any degree of accuracy. In regard to the number 

 of the chromosome-like granules, no general conclusion can be made 

 as yet; however, there are some indications that the number is four 

 large or eight small ones (pi. 3, figs. 64-68). If a chromatin granule 

 is present at the posterior end of the axostyle there is likewise a con- 

 striction of it into two parts when the axostyle divides. 



The question whether the flagellum splits in Crithidia leptocoridis 

 to form two as found by Porter (1910) in Crithidia melophagia, or 

 whether there is a new outgrowth from the basal granule as described 

 for Herpctomonas nmscae domesticae by Wenyon (1913), can not be 

 answered definitely as yet. Observations of the living material would 

 go to show that it is a process of splitting rather than a new outgrowth. 

 The stained preparations also tend to confirm this. 



