STUDIES ON FARASITTC PROTOZOA. 
459 
Studies on Parasitic Protozoa. 
II. (a) The Encystment of Rhizomastix gracilis Alexeieff ; 
(b) Tetr atrichomastix parisii n. sub-gen., n. sp. 
By 
Doi'iis Li. M»ckiniioii, 
(Assistant in the Zoology Department, University College, Dundee). 
With Plates 31 and 32. 
Introduction. 
The intestine of that common grub^, the larval Tipula, con- 
tains a rich bacterial flora^ at the expense of which there 
flourish a surprising number of protozoa. Among these are 
at least eight flagellates and two amoebae.^ 
It is customary to speak of such an intestinal fauna as para- 
sitic, a word which implies that these organisms are in some 
sort harmful to their host. A short study of the actively 
moving and actively feeding protozoa in the gut of the crane- 
fly larva suggests much rather that the work they do in scav- 
enging, and in keeping down the vast quantities of bacteria 
that threaten to choke the passage-way of the intestine, quite 
outweighs any trifling inconvenience that their presence 
might possibly cause the host. The largest and healthiest- 
^ Leger (1892) recorded three gregarines. I have already recorded, 
ill a preliminary note (‘Parasitology,’ 1912), the following flagellates 
from Tipula: Trichomastix sp., Monocercomonas melolonthse 
(Grassi), Polymastix melolonthse (Grassi), Hexamitus intesti- 
nalis Duj., Embadomonas agilis Mackinnon, and E. alexeieffi 
Mackinnon. To these I would now add Rhizoniastix gracilis 
Alexeieff and Tetratrichomastix parisii, n. sub-gen., n. sp. A 
paper dealing with the amoebai is at present in preparation. 
