160 University of California Publications in Zoology [VOL. 19 



20 and 21. In figure 20 the binucleated appearance of the nucleus and 

 buds is very prominent. The chromatin granules have a paired effect 

 which is difficult to interpret. In figure 21 a more complex structure 

 is represented. Anterior to the nucleus there is a group of five 

 endogenous buds. Two of these, owing to their position, are not de- 

 stained sufficiently to make clear their nuclear structure. This large 

 flagellate has a sharply defined parabasal body and flagellum, similar 

 to those in figures 19 and 20. The large size of such forms has aided 

 materially in the interpretation of the endogenous buds, which, upon 

 developing, form the so-called zooids. 



The most mature stage of endogenous budding yet found, wherein 

 the resulting zooids are still within the periplast, is pictured in 

 figure 22. There are approximately twelve clearly defined zooids 

 massed near the central part of this large flagellate. The structure 

 of the zooids could be studied readily. The nucleus and parabasal 

 body in each, because of their deep stain, helped to distinguish the 

 several zooids. The other organelles were not visible. Another inter- 

 esting feature concerning these zooids is the difference in the stages 

 of their development. Some are larger and more mature and were 

 doubtless budden off from the nucleus first. Probably the zooids of 

 the flagellate have been retained within the periplast of the parent 

 for a longer period than usual. If the size of these zooids be compared 

 with that of the free zooids shown in figure 23 the former, on the 

 whole, are larger and more fully developed. There are, moreover, 

 no marked signs of degeneration of the parabasal body, of the flagel- 

 lum, or of the cytoplasm. The parabasal body is almost hidden by 

 the zooids in that region. 



The final step in the endogenous-budding process comes with the 

 degeneration of the body-plasm of the parent flagellate, leaving a mass 

 of zooids, together with the flagellum and parabasal body of the parent. 

 Portions of smears have been observed to be literally covered with 

 zooids and discarded flagella. As degeneration proceeds the parabasal 

 bodies next disappear, and finally the flagella, leaving only numerous 

 zooids of various sizes and structure. The last phase is the one most 

 frequently observed in preparations of Crithidia euryophthalmi. I 

 had been working with C. euryophthalmi more or less for a period 

 of almost two years before the clue as to the origin of these small 

 zooids was found. It had been most puzzling to find so many of these 

 small, non-flagellated, binucleated forms (pi. 4, fig. 40), which were 

 obviously unlike the initial infective spores (pi. 2, figs. 1, 2). They 



