EFFECTS OF CARBON DIOXIDE 539 
tubes of angiosperms, found decided specific differences. Many 
other scattered observations exist, which however, it is difficult 
to compare on account of the different methods employed in 
obtaining them. 
It is interesting to consider the results here obtained in con- 
nection with those of Jennings and Moore (’01) on the chemotactic 
effect of carbon dioxide on various protozoa. Of the four forms 
mentioned by them as being attracted by this substance, three 
(i.e., Paramecium caudatum, Colpidium colpoda, and Chilomonas 
paramecium) have been studied in these experiments and all show 
marked powers of resistance, as well as a strong negative response 
when the concentration is suddenly made high in the edges of the 
drop. Of the forms found by them to be indifferent, unfortu- 
nately only two genera (Euglena and Euplotes) were available, but 
these both showed a relatively low resistance as compared with 
related forms, at least so far as the continuance of locomotion is 
concerned. It would be interesting to study the other members 
of their list in this connection. Doubtless many other facts of 
behavior could be brought into line with such physiological pecu- 
liarities as the one under consideration. 
One of the most interesting results that appears from these 
experiments is the striking difference that seems to exist between 
the contractile elements of the cell—the myonemes—on the one 
hand, and the vibratile ones—cilia, membranelles, and flagella 
on the other. The former are very quickly thrown out of func- 
tion while the latter continue their normal movements for a long 
time. The best illustration of this point is Vorticella, in which 
the contractile filament of the stalk, and the myonemes, after a 
primary stimulation, are inside a minute or less completely para- 
lyzed, while the membranelles perhaps after stopping for a short 
time continue to beat for three-quarters of an hour. Such results 
are in agreement with those obtained by other workers. Nere- 
sheimer (’03), for example, found that the myonemes and mem- 
branelles of Stentor are differently affected by substances like 
morphin, which paralyze the former and do not affect the latter. 
Lillie (’12) has observed that the cilia of Arenicola larvae continue 
their acvitity for hours in isotonic sugar or magnesium chloride 
