1919] McCulloch: Life Cycle of Crithidia and Trypanosoma 161 



were smaller in size, their periplast was thinner, and they destained 

 much more rapidly after iron-haemotoxylin. Serial sections of the 

 mid-stomach showed them grouped in pockets between the epithelial 

 cells. Possibly the endogenous process occurred there or they were 

 lodged there as the current of food carried the others down into the 

 pyloric expansion. They could be arranged in a series, beginning 

 with those averaging about 1.7/x, in length (pi. 4, fig. 40) and gradating 

 to the size of the spores which were regarded as the initial infective 

 spores (pi. 2, fig. 1; pi. 4, figs. 40-54). 



The development of the endogenous buds into binucleated zooids 

 is not easy to interpret. In figure 23, plate 2, the numerous zooids 

 present variations in both size and structure. Unlike the latent bodies 

 of Trypanosoma gambiense of Moore and Breinl (1907) and the endo- 

 genous buds of Leptomanas pattoni of Minchin and Thomson (1915), 

 these endogenous buds show no central chromatin granule within the 

 nuclear membrane. Their chromatin is distributed at the periphery 

 of the nucleus usually in one of three ways. In the elongate flagellates 

 (pi. 2, figs. 11, 14, 19) the buds have their chromatin material massed 

 irregularly on the nuclear membrane. A second form of peripheral 

 chromatin in the nucleus is a noticeable mass or granule at one point. 

 This is characteristic of the buds within the pear-shaped flagellates 

 (pi. 2, figs. 15-18). The third type of nuclear structure in the buds 

 is possibly only a slight modification of the others. In figure 20, 

 plate 2, the internal or endogenous buds appear to be binucleated 

 because of the peculiar segregation of the chromatin material on the 

 nuclear membrane. At present these several modifications of the 

 nuclear structure are not regarded as having any special sequence or 

 significance. In some of the smallest zooids of figure 23 there are 

 still other modifications wherein a single, deeply staining mass is fre- 

 quently observed. Owing to the size of these zooids it is extremely 

 difficult, even with a binocular microscope, to form any adequate 

 conception of their structure. 



A diligent search has been made among these small forms to find 

 a series of developing zooids which would clearly show the whole 

 process of the formation of the several organelles. While Crithidia 

 euryophthalmi undoubtedly furnishes the necessary material for such 

 a study, the size of the endogenous buds makes the interpretation 

 exceedingly difficult. It is therefore disappointing that a complete 

 series has not yet been accumulated showing the steps which are 

 thought to take place in the development of a bud into a typical 



