EXPLANATION OF PLATES 



All figures were outlined with a camera lucida using a ^ objective on the 

 binocular microscope and a Watson no. 20 holoscopic eye-piece. The magnifica- 

 tion is in all cases approximately 3500. Unless otherwise stated all figures were 

 made from iron-haematoxylin preparations. 



PLATE 2 



Crithidia euryophthalmi from the ' ' crop ' ' of Euryophthalmus convivus. 



Fig. 1. Small, oval infective spore which has been casually ingested with 

 food. This spore shows the structure common to these phases, thick periplast, 

 deeply staining nucleus in extreme posterior end, heavily stained parabasal 

 body. Faint nuclear rhizoplast. 



Figs. 2-8. A series of developing crithidias showing successive stages of 

 development. Both anterior and posterior ends are becoming attenuate. The 

 nucleus changes from a solid mass of chromatin to a vesicular nucleus, chro- 

 matin-encrusted membrane and central karyosome. Flagellum grows forward 

 and carries anterior end of body along with it, which forms undulating membrane. 



Figs. 9-10. Two mature flagellates illustrating extremes in length, width, 

 and shape, common to C. euryophthalmi. A whole series of intergrading forms 

 occur between these two extremes. 



Figs. 11-23. Multiple fission; endogenous budding. (Fig. 11). Flagellate 

 with a nucleus, two endogenous buds posterior to nucleus. Chromatin of both 

 nucleus and buds massed on nuclear membrane. Blepharoplast and parabasal 

 body intact, no indications of division. 



Fig. 12. A short flagellate; one endogenous bud; chromatin peripheral in 

 each nuclear structure. 



Fig. 13. Flagellate with three clearly defined nuclear structures and the 

 beginning of a third bud from the most anterior, the nucleus proper. Chromatin 

 peripheral in each of these nuclear structures. 



Fig. 14. Elongate flagellate nucleus; two endogenous buds anterior to the 

 nucleus; chromatin peripheral. 



Figs. 15-17. Pear-shaped crithidias with endogenous buds. If nucleus be 

 present in each there are no differences in structure between nucleus and bud. 

 Buds in these flagellates are always sharply defined. Chromatin material on 

 membrane but most of it is in definite granules. 



Fig. 18. Pear-shaped form with numerous endogenous buds but no definite 

 nucleus. First stages of degeneration present, parabasal body has disappeared 

 and only a fragment of discarded flagellum is near. Chromatin peripheral 

 but also in form of one granule. 



Fig. 19. Elongate flagellate; two endogenous buds posterior to nucleus. 

 Nuclear rhizoplast still present. Chromatin distributed irregularly on the 

 nuclear membranes. 



Fig. 20. Elongate flagellates with nucleus and two endogenous buds; chro- 

 matin massed in the anterior and posterior portion of each nuclear structure. 

 Parabasal body has taken no part in this multiple fission. 



Fig. 21. Large endogenous flagellate with five buds, all anterior to nucleus 

 proper. Two of the buds are not destained sufficiently to see their structure. 

 The organelles other than nucleus have taken no part in the process of endo- 

 genous budding. Flagellum, blepharoplast, parabasal rhizoplast and parabasal 

 body are still intact and clearly shown. 



Fig. 22. Late stage in endogenous budding. Buds have formed zooids, 

 each of which has a nucleus and a second, deeply-staining structure anterior 

 to nucleus. Flagellum, parabasal body, parabasal rhizoplast, and the blepharo- 

 plast are still intact. No signs of degeneration are to be observed in this 

 flagellate. 



Fig. 23. Drawing made from a field literally covered by discarded flagella 

 and small zooids. The blepharoplast and parabasal body are still attached to 

 8ome of the flagella, Zooids show various stages of nuclear structure. Some 

 have a single mass of chromatin, others two granules within a chromatin-en- 

 crusted membrane. Some few of the zooids contain a nucleus, nuclear rhizo- 

 plast, and a second mass of chromatin anterior to these. 



[182] 



