With regard to the contractility of the myunemes, no detailed explanation 

 can be offered at present. Biitschli (37) has shown the possibility of explaining 

 the contractile mechanism of such structures by differences in surface-tension 

 arising between the walls and the contents of protoplasmic alveoli which 

 are disposed with a definite arrangement. 



(b) Other Forms of Energy. Light-production or phosphorescence 

 is a common phenomenon in marine Protozoa, a property expressed 

 in such names as Noctiluca (p. 279) and Pyrodinium (p. 278). The 

 magnificent phosphorescent effects often seen at night, especially 

 in warmer seas, is to be referred chiefly to swarms of Protozoa. 

 The source of the luminosity appears to reside in small globules of 

 fat or oil, and is probably the result of oxidation. It is easy to 

 observe that the production of light is stimulated by agitating or 

 stirring the water. For a general discussion of luminosity in living 

 organisms, see Putter (200). 



From the analogy of the known facts in the physiology of animal 

 and plants, it may be inferred that in Protozoa also the vital 

 activities are accompanied by the production of heat and by 

 electrical changes ; but no exact determinations of such changes 

 have been ma"de. 



5. Reactions to Stimuli and Environment. It can easily be 

 observed that Protozqa react in a definite manner to stimuli, and 

 behave in a particular way under certain conditions. In most 

 cases, however, these responses to external conditions must be 

 regarded as fundamental properties of the living protoplasm, and 

 hot as functions of specially differentiated organs of the body. 

 This is well seen, for example, in amoebae, some species of which are 

 very sensitive to light, and cease feeding when exposed to the 

 bright illumination of the stage of the microscope (Rhumbler, 34). 

 In Arcetta the nuclear division is stated to take place only at night, 

 between 1 and 5 a.m. (Khainsky, 145). In such cases, however, 

 there is nothing which can be identified as a special light-perceiving 

 organ. 



In other cases Protozoa may possess organs which must be regarded 

 as sensory in nature. Pseudopodia appear to possess in many cases 

 a tactile or sensory function to a marked degree, and sometimes to 

 be specialized for such rfunctions, as, for example, the anterior 

 pseudopodia of some Myxosporidia, such as Leptotheca agilis 

 (Fig. 165). The same is true to a much greater degree of flagella 

 and cilia ; anteriorly-directed flagella are perhaps always sensory in 

 function, especially when they are not the sole means of locomotion, 

 as in such forms as Rhizomastigina (p. 268) or Bodonidce (p. 270) ; 

 and in many Ciliata stiff tactile bristles occur (p. 446). In many 

 flagellates organs are found which appear to be specially sensitive 

 to light, in the form of pigment-spots or stigmata, which are 

 described further below. 



