466 
DORIS L. MACKINNON. 
there is still considerable difference of opinion as to the 
systematic value of the flagellar apparatus. On the one 
hand^ Doflein (1911) considers that the genera Tricho- 
monas and Trichoma stix are just varieties of the same 
form, of which the recurrent flagellum is attached to the 
body-wall in the first case, while it remains free in the 
second. On the other hand, there are those, like Parisi 
(1910), who think that the number and mode of attachment of 
the flagella are points of real value to the classifier of these 
organisms. Parisi, accordingly, has split up the genus 
Trichomonas Donne into three sub-genera : 
(1) Trichomonas sensu stricto, with three anterior 
flagella, and an undulating membrane. 
(2) Tetrat richomonas, with four anterior flagella, and 
an undulating membrane. 
(3) Trichomastix, with three anterior flagella, and one 
recurrent flagellum, which does not adhere to the body to 
form an undulating membrane. 
The flagellate which I am about to describe from Tipula, 
while undoubtedly a trichomonad, falls into none of these 
three sub-genera. It is provided with five flagella, of which 
four are directed forwards, and the fifth is a Schleppgeissel,’’ 
as in Trichomastix. This form, then, bears exactly the 
same relations to Trichomastix that Tetratrichomonas 
has to Trichomonas.^ I propose to place it in a fourth 
sub-genus, Tetratri choiiiastix. This seems the simplest 
method of proceeding, so long as we abide by the present 
classification of the trichomonads. 
To subdivide the genus is certainly a convenience, and the 
characters on which the subdivision is based seem clear 
enough. What is less satisfactory are the species within 
these sub-genera. I have already expressed my scepticism 
with regard to what may be called host-species in para- 
sitic protozoa. Some authors consider that flagellates should 
1 A true Trichomastix with three anteriorly directed flagella, 
indistinguishable from T r i c h o m a s t i x t r i c h o i) t e r o r u m , Mackinnon, 
also occurs in Tipula (see Mackinnon, 1912^ 
