534 MERKEL HENRY JACOBS 
killed the protoplasm becomes brownish and opaque, doubtless 
due to coagulation phenomena. 
B. Flagellates 
1. Peranema trichophorum. This form shows conditions which 
suggest those already noted in Vorticella. As is well known, 
Peranema has a single very prominent flagellum, which in loco- 
motion is directed straight forward. Ordinarily it is quite rigid 
except the tip, whose movements cause a slow forward progres- 
sion of the animal. During progression, and also when otherwise _ 
at rest, the body shows very decided changes in form, these ‘meta- 
bolic’? movements, or contortions, being one of the most striking 
characteristics of the species. When exposed to carbon dioxide 
Peranema responds perhaps as quickly as any of the forms studied. 
Its forward progression ceases almost instantly and after a few 
preliminary, and rather vigorous contortions, the body suddenly 
becomes paralyzed in whatever state of contraction it may hap- 
pen to be in at the time. Only rarely does the animal have time 
to contract to a spherical form before being overtaken with this 
paralysis; consequently the typical appearance of the body is an 
irregular mass which does not change its form so long as the stream 
of carbon dioxide is allowed to flow. 
The flagellum responds differently. Contact with the carbon 
dioxide causes it to beat with a swinging motion in which the proxi- 
mal as well as the distal portion is concerned. Sometimes these 
movements are rather vigorous, but they never give rise to loco- 
motion. They may continue with more or less uniformity for a 
half or even three-quarters of an hour; at the end of that time the 
flagellum gradually comes to rest. All visible movements have 
now ceased, but the animals are not necessarily dead. Experi- 
ments were tried to determine what powers of recovery Peranema 
possesses after becoming perfectly motionless. It was found that 
when the drop containing them is removed from the gas chamber 
and placed in contact with the air, a considerable percentage 
of the individuals may recover after an exposure of an hour and ~ 
a quarter to carbon dioxide, even though all movements have for a 
