PHYSIOLOGY 



113 



a-d). In the Protociliata and the majority of holotrichous and 

 heterotrichous cOiates, the ciHa are arranged in longitudinal, or 

 oblique rows and it is clearly noticeable that the cilia are not beating 

 in the same phase, although they are moving at the same rate. A 

 cilium (Fig. 47, e) in a single row is slightly in advance of the cilium 

 behind it and shghtly behind the one just in front of it, thus the cilia 

 on the same longitudinal row beat metachronously. On the other 

 hand, the cilia on the same transverse row beat synchronously, the 

 condition clearly being recognizable on Opahna among others, 

 which is much like the waves passing over a wheat field on a wind}^ 



,,i 



/'"^^ 7 



1 2 





w/'r.i^im^^^ii 



Fig. 47. Diagrams illustrating ciliary movements (Verworn). a-d, 

 movement of a marginal cilium of Urostyla grandis (a, preparatory and 

 b, effective stroke, resulting in rapid movement; c, preparatory, and d, 

 effective stroke, bringing about moderate speed) ; e, metachronous move- 

 ments of cilia in a longitudinal row. 



day. The organized movements of cilia, cirri, membranellae and un- 

 dulating membranes are probably controlled by the neuromotor 

 system (p. 54) which appears to be conductile as judged by the 

 results of micro-dissection experiments of Taylor (p. 57). 



The Protozoa which possess myonemes are able to move by con- 

 traction of the body or of the stalk, and others combine this with the 

 secretion of mucous substance as is found in Haemogregarina and 

 Gregarinida. 



Irritability 



Under natural conditions, the Protozoa do not behave always in 

 the same manner, because several stimuli act upon them usually in 

 combination and predominating stimulus or stimuU vary under dif- 



