The Mastigophora 173 



apparently joined to the blepharoplast. In Mastigina the nucleus is an- 

 terior as in Mastigamoeha and is joined to the blepharoplast, but slender 

 pseudopodia seem to be lacking. The nucleoflagellar relationships of 

 Mastigina liylae (Frenzel) Goldschmidt have been described by Becker 

 (12). In addition to the flagellum, two other structures are joined to the 

 blepharoplast (Fig. 4. 39, J). A rhizostyle extends posteriorly, and a cap- 

 shaped "cape" fits over the anterior surface of the nucleus. From the cape, 

 filaments extend to the anterior end of the body. 



Rhizornastix gracilis Alexeieff, recovered from an axolotl and from 

 crane-fly grubs, shows a rhizostyle, extending almost to the posterior end 

 of the body (Fig. 4. 39, G), but there is no "cape" as in Mastigina hylae 

 and the nucleus is central (191). Nuclear division occurs within the cyst 

 (Fig. 4. 39, H), and a second rhizostyle develops by outgrowth from a 

 blepharoplast. 



HeJiobodo (Fig. 4. 39, I) includes spheroid uninucleate organisms with 

 two flagella and many slender pseudopodia which apparently are not 

 axopodia. Whether this genus actually belongs in the Rhizomastigida is 

 uncertain. 



Histomonas meleagridis Tyzzer (Fig. 4. 39, A-F) is associated with 

 "blackhead" (enterohepatitis) in turkeys and chickens. An interesting 

 featiue of blackhead in turkeys is that young birds are readily infected 

 by feeding them embryonated eggs of the cecal worm, Heterakis gallinae. 

 The flagellates apparently remain viable in such eggs for more than a 

 year when kept in a refrigerator (189). H. meleagridis is an amoeboid or 

 slug-like organism which may produce slender pseudopodia and is ca- 

 pable of changing shape rapidly (20). Some of these slender pseudopodia 

 may correspond to the tubular protrusions (Fig. 4. 39, E) noted by Wen- 

 rich (280) in stained preparations. The unusual variability in number of 

 flagella raises questions concerning the validity of Histomonas meleagridis 

 as a specific name for all the various strains described from birds. One 

 flagellum is typical in cultures from chickens (20), although binucleate 

 forms with two flagella, and tetranucleate forms with four, occur occa- 

 sionally. In material from ring-neck pheasants (280), flagellate stages 

 nearly always showed four flagella. Flagellar resorption occurs at an early 

 stage of nuclear division so that non-flagellated uninucleate and bi- 

 nucleate forms are common and tetranucleate stages without flagella are 

 sometimes seen (20). Whether the "rhizostyle" is a normal organelle, or 

 merely an occasionally observed remnant of the paradesmose is still un- 

 certain. 



Order 2. Protomastigida 



These are relatively small organisms with one or two flagella. The 

 body is typically plastic, but not markedly amoeboid. Nutrition is sapro- 

 zoic in some types and holozoic in many others. The order includes 



