86 C. CLIFFORD DOBELL. 
makes its way into the cytostome, and gets its end stuck fast 
init. In this case the monad may swim about for a con- 
siderable time with the rod sticking out of its mouth, present- 
ing a curious appearance to the observer. 
Subsequent changes in the ingested food masses are most 
easily seen in organisms stained intravitam with neutral red. 
It can then be seen that the following series of events takes 
place: At first minute particles are seen in the protoplasm 
at the bottom of the cytopharynx. They appear to he freely 
in the cytoplasm, without any vacuole surrounding them. 
After a time the particles are found to have agglutinated, 
and are enclosed in vacuoles. Digestion now takes place, and 
the agglutinated masses are gradually eroded. By means of 
neutral red the different stages of digestion are very beauti- 
fully demonstrated. Ingested particles at first stain a bright 
red. In the food vacuoles the food bodies also take up the 
stain strongly, but they are coloured reddish-orange. Later 
stages are usually of an orange or yellowish hue; so that the 
posterior end of the organism may contain food balls of 
different colours of red, orange and yellow—the colour 
corresponding with the stage which the digestive process 
has reached. It may be inferred that the digestive juice is 
neutral in reaction, but becomes somewhat alkaline as diges- 
tion proceeds. The change of colour may also be due partly 
to reduction. (Neutral red becomes yellow with alkali, to 
which it is exceedingly sensitive, and is reduced to a colourless 
leuco-product.) 
The whole process, as I have observed it in Copromonas, 
bears a close resemblance to that described and figured in 
Paramcecium by Prowazek (383). 
Stokes (49) has described the ingestion of food by means of a 
“mouth ” in Petalomonas, a genus which, as I have already 
pointed out, is probably closely allied to the form under con- 
sideration. The method of feeding seems to be identical in 
the two genera. 
As regards the larger euglenoids, much doubt still exists 
regarding the function of the so-called “ mouth.” Although 
