Physiology 493 



and in creeping the characteristic gyration or swerving occurs in a par- 

 ticular direction presumably determined by structure of the body. The 

 reactions of amoeboid organisms are less complicated in that locomotion 

 is by "creeping," without the rotation and gyration characteristic of 

 freely swimming flagellates and ciliates. Changes in direction are brought 

 about by formation of new pseudopodia at a different point on the body 

 surface. 



Responses to light 



The reactions of Protozoa to light have been reviewed by Mast 

 (380, 388). The stimulating intensity of light varies with the wave length 

 as well as with the intensity of illumination. Within the visible spectrum, 

 light at about 485 mjjs, produces the maximal effect on species of Chlamy- 

 domonas, Euglena, Goyiium, Pfnicus, and Traclielomonas, while light at 

 535 mjji is most effective for Eudorina, Pandorijin, and Spondylomorum 

 (381). The stimulatory spectrum for Volvox (309) is similar to that for 

 Euglena. Many flagellates — species of Euglena, Chlamydomonas, Crypto- 

 7nnnas, and Goniwn, among others — react so that the path of locomotion 

 is definitely oriented to the source of light. Others, such as Peranema, 

 may show merely a shock reaction which is not followed by definite 

 orientation. Species of Euglena (248, 380) respond to a sudden change in 

 the intensity of illumination by their characteristic motor reaction, and 

 the response is repeated until the stigma is equally illuminated at each 

 point in the spiral path of locomotion. As a result, photopositive speci- 

 mens swim toward the source, and photonegative specimens away from 

 the source of light. Illumination of Amoeba proteus (386), which is pho- 

 tonegative in strong light, causes an increase in thickness of the plasmagel 

 by inducing gelation of the adjacent plasmasol in the stimulated region. 

 This increase in elastic strength causes a contraction of the plasmagel in 

 the stimulated area. Therefore, the formation of pseudopodia in this 

 region is inhibited and new pseudopodia will tend to develop at the op- 

 posite end of the body. A small increase in illumination may do nothing 

 more than retard temporarily the growth of a pseudopodium. The result 

 of the first type of reaction is a photonegative response, while the second 

 type produces only a delay in locomotion. The photonegative Stentor 

 coeruleus (248, 380), one of the few ciliates known to react definitely to 

 light, shows a typical motor reaction to increased illumination, and the 

 response is repeated until the organism is equally illuminated through- 

 out its spiral course and is moving away from the source of light. 



Reactions to electric current 



Although reactions to the electric current can scarcely be con- 

 sidered part of the adjustment to natural environments, many Protozoa 

 show rather specific responses. In the genus Amoeba, reactions vary with 



