530 MERKEL HENRY JACOBS 
move about in a fairly normal manner appear to take no food, 
and the food vacuoles present at the beginning of the experiment 
gradually are lost until the bodies of the organisms become re- 
markably transparent. Fora long time there is no swelling of the 
body, but rather a narrowing, doubtless due to the loss of the 
food vacuoles; towards the last there may be a certain amount of 
swelling but the pellicle very rarely ruptures as it does in various 
species of Paramecium. 
5. Coleps hirtus. This species forms a marked contrast with 
the preceding, being the least resistant of all the ciliates studied. 
Even the most resistant individuals hardly approach the least 
resistant ones of the other forms. The effect of the carbon diox- 
ide is seen almost instantly. The animals show no decided nega- 
tive reaction, apparently being overcome too quickly for such to 
occur. The normal, rather active movements of locomotion cease 
within a few seconds and thereafter only irregular ‘vibrating’ 
movements occur up to the time of death, of which the average is 
well under five minutes. Even the most resistant individuals do 
not live for ten minutes. The visible effects of the carbon dioxide 
are greater on this form than any of the others studied. The 
barrel-shaped body swells until it is broadly elliptical or even 
circular in outline, the increase in volume being very decided. 
At the same time the plates of the armature*become indistinct 
and disappear, giving the appearance at least of actually being 
dissolved away. In consequence the body becomes very trans- 
parent and the protoplasm may be seen to undergo coagulation 
phenomena. The cilia sometimes beat after the armature has 
partly or entirely disappeared but usually their movements cease 
early. The cell in most cases bursts, generally at one of the ends; 
sometimes this occurs in two or three minutes, before much swell- 
ing has taken place. 
6. Blepharisma lateritia. This on the whole is a very resistant 
form, being second only to Colpidium in this respect. Itshows, 
however, rather more individual variation in the same culture 
than most of the other forms studied, isolated individuals some- 
times succumbing quite early. Strangely enough, in spite of its 
general resistance its movements are very quickly affected. At 
