1922] McDonald: On Balantidium coli and Bakintidium suis 291 



the case of Balantidium the entire organism, with the exception of 

 the oral plug, is covered with cilia. So the sliglitlj' lesser degree of 

 specialization in the neuromotor apparatus would be the logical expec- 

 tation if modification of mtracytoplasmic structures is ' correlated 

 with modification of external structures with which they have a direct 

 coimeetion or of which they form an integral part. 



Prom the point of view of eiBciency, also, the arrangement in 

 Balantidium is readily explainable. The locomotor activities of the 

 organism may be separated into three main sorts, swimming, feeding, 

 and boring, this last very likely being used in penetration of the 

 intestinal wall of the host. In swimming the coordination of the entire 

 locomotor apparatus is necessary. In feeding, and in boring, particu- 

 larlj-, the coordination of the adoral cilia with those of the apical cone 

 is extremely essential. Such coordination would be most effectively 

 brought about by a direct connection of the parts concerned, and this 

 direct connection is accomplished by the uniting of all of the rootlets 

 of the cilia of these two regions by means of the radial fibers, without 

 the interpolation of the motoriiun. 



Throughout the above discussion the assumption of a neural func- 

 tion for the neuromotor apparatus, i.e., the power of conductivity of 

 stimuli resulting in coordination of parts, has been based on two 

 general types of evidence, morphological and experimental. The 

 chemical evidence, that is, the affinity for acid fuchsin, as presented 

 by Sharp (1914) for Diplodiivium and by Yocom (1918) for Euplotes, 

 seems slightly less convincing in the case of Balantidium,. In the last 

 named organism not only does the micronucleus, which has no connec- 

 tion with the neuromotor apparatus, show an affinity for acid fuchsin 

 but so also do certain cytoplasmic inclusions, which if not food par- 

 ticles are at least undoubtedly concerned in some way with metabolism 

 and have no morphological relation to the neuromotor apparatus. 

 Yocom (1918) states that there is more of the orange G in the micro- 

 nucleus giving it a different shade from the parts of the neuromotor 

 apparatus in the case of Euplotes; but in Balantidium I have been 

 unable to detect any such differentiation. 



Morphological evidence for attributing neural function to the 

 neuromotor apparatus has been clearly presented by Yocom (1918) 

 in his discussion of the apparatus in Euplotes. The evidence found 

 in Balantidium is not strikingly different. There is in the latter 

 organism the same intricate relationship between the neuromotor 

 apparatus and the motor organelles. The most active cilia, i.e., the 

 adoral cilia, are directly connected by the adoral ciliary fiber with 



