SOIL PROTOZOA. 315 



of the body. Seen from the ventral aspect — i. e., from the side 

 on which the flagella arise (text-fig. 1) — the groove proceeds from 

 I'ight to left, and then curves round to the dorsal surface and 

 reaches the posterior end of the body. If the body is of normal 

 length there is only this one turn in the spiral, but if the 

 organism is elongated there may be two turns. The accom- 

 panying text-figure, drawn from a specimen immediately after 

 killing with osmic-acid vapour, shows the shape of the organism, 

 the position of the groove, and the disposition of the flagella. 

 The latter aie arranged in two pairs — a shorter anterior pair and 

 a longei' postei'ior pair. The a,nterior pair is direc^d forwards 

 dui'ing motion and the posterior pair is trailed backwards. 



Text figure 1. 



Tetramitus spiralis. 

 Outline drawing as seen in ventral view, showing tlie relations of tlie groove ((?.)• 



The members of each pair are frequently very closely applied, 

 and often appear as one thick flagellum. When in active 

 movement, which is caused by the lashing of the anterior pair 

 of flagella, the organism progi-esses very rapidly and rotates on 

 its long axis. The posterior pair of flagella appears to lie 

 within the groove and extends beyond the posterior end of the 

 organism, which swings from side to side of the line of motion 

 owing to the rapidity of progression. The mouth is very 

 difficult to locate, being ill-defined, but in certain examples I 

 have made out its position a short distance from the anterior 

 end as a depression in the groove. Bacteria are ingested and no 



