ZOOMASTIGINA 65 



causes of sleeping sickness in man when they have passed into the 

 cerebrospinal fluid, and T. brucet, the cause of African cattle sickness, 

 are non-pathogenic in antelopes. Their crithidial stage is passed in the 

 salivary glands of the tsetse (Glossina), reproduces by binary fission, 

 and is not intracellular. They are transmitted to the vertebrate host 

 by the bite of the fly. 



Choanoflagellata (or Choanoflagellidae) . Uniflagellate, generally 

 fixed, forms; with a protoplasmic collar around the base of the flagel- 

 lum. Ingestion by attraction of particles by the flagellum to the outside 

 of the collar, adherence to this, and transference by streaming of 

 protoplasm to the base of the collar, where they are received by a 

 vacuole which is formed between the cuticle, if present, and the proto- 



'■■f-vac. 



Fig. 49. Choanoflagellata. A, Monosiga brevipcs, x 1200. B, Codosiga um- 

 bellata, x 310. Both after Saville-Kent. C, Ingestion in Codosiga. f.vac. 

 food vacuole. The dotted lines show the currents set up by the flagellum, 

 the small arrow the transport of the food particles on the collar. 



plasm (Fig. 49 C): defaecation within the collar. There is usually a 

 stalk, generally not of living matter. This may branch, and thus unite 

 numerous zooids. Examples are Monosiga (Fig. 49 A), solitary, with 

 protoplasmic stalk; Codosiga (Fig. 49 B), branched, with cuticular 

 stalk. 



Order POLYMASTIGINA 



Zoomastigina with two to many, generally with more than three, 

 flagella, and an extranuclear division centre. 



The genera here placed in one order are usually separated as Poly- 

 mastigina, Hypermastigina, and Diplomonadina. They are the most 

 highly organized members of the Mastigophora. 



Trichomonas (Fig. 50). (One of the Polymastigina sensu stricto.) 

 Body roughly egg-shaped ; with four flagella, of which one is directed 



