14 Univvrsify of California Publications in Zoology [Vol. 20 



Even the reproductive phases of binary and multiple fission 

 retain the elongated form characteristic of the trophozoite, thus per- 

 mitting those stages to retain their position among the segregated 

 parasites of their own kind. In other polymastigotes, such as Tricho- 

 monas, the stage of multiple fission is an amoeboid Plasmodium, a 

 rounded-up, somewhat shapeless amoeboid mass (Kofoid and Swezy, 

 1915). In Streblomastix, however, the linear form persists through- 

 out this phase, in so far as we have observed it, although it shows 

 greater laxity of form and less torsion (pi. 2, figs. 14, 15) than do 

 the vegetative trophozoites. Thus in every feature of its structure and 

 phase of its life history Streblomastix is intimately adapted to its 

 pecviliar parasitic mode of life notwithstanding its seeming simplicity 

 of strixcture. 



RELATIONSHIPS 



The presence of six flagella definitely allocates Strehlomcistix in the 

 Order Polymastigina. Its relative simplicity of structure as com- 

 pared with most genera of this order is shown by the undifferentiated 

 condition of the flagella. There is no single specialized trailer at- 

 tached as an undulating membrane, and none intraeytoplasmic as an. 

 axostyle. 



The presence of the four longitudinal spiral ectoplasmie "myon- 

 emes ' ' or extensions of the neuromotor apparatus is very suggestive of 

 a relationship to the Trichonymphidae in most of which such lines 

 arise from the blepharoplast and are the stems from which spring the 

 many so-called cilia. This relationship will be more evident on 

 detailed comparison. There are eight such lines in Dinenympha 

 gracilis (Leidy, 1881) along the course of each of which small cilia 

 take their origin, but there are no developed anterior flagella. Zulueta 

 (1915) has shown that these extend posteriorly as free flagella and 

 that they are grouped four and four on the daughter centrosomes at 

 the poles of the spindle at mitosis. The species upon which Zulueta 

 worked appears to be the same as that figured by Grassi and Sandias 

 (1893, pi. 5, figs. 18-20) which Grassi and Foa (1911 ) later distinguish 

 from Leidy 's species as Spirotrichonympha. Pyrsonympha vertens 

 (Leidy, 1881 and Porter, 1897) likewise has eight such lines arising 

 from the blepharoplast with small lateral cilia arising from them. 

 Anteriorly there is a blepharoplast from which a free slender thread 

 extends anteriorly into the host cell not unlike the rhizoplast-blepharo- 



