EDMONDSON — PROTOZOA OF IOWA. 9 



while the simplicity of the structure reminds the thoughtful stu- 

 dent that before his eyes is life reduced to its lowest terms. 



In the formation of pseudopodia the ectoplasm is thrust out in 

 digitate processes from various points of the periphery, to be closely 

 followed by the granular endoylasm in a streaming movement. 



Biitschli, and more recently Rhumbler, announced that as the 

 endoplasm advances in a median axis toward the end of the newl}^ 

 formed pseudopodium, it flows outward and streams back along 

 the inner surface before coming to rest. That such a backward 

 flow does not take placs has been clearly demonstrated by Jen- 

 nings, the results of his observations being recorded in the sixth 

 paper of "Contributions to the Study of the Behavior of the Lower 

 Organisms." The cause for the formation of pseudopodia has 

 been attributed by Verworn to the introduction of oxygen into 

 the molecules at the surface of the body thereby reducing cohe- 

 sion, the result being that surface tension is reduced. This obser- 

 vation is of no little significance from a biological point of view as 

 it is believed that highly specialized muscular movements are but 

 modifications of such a movement as is expressed in the pseudo- 

 podium of Anuvba. 



There are no fixed distinctions between the regions of Anuvba 

 proteus, but at times what maybe termed an anterior and posterior 

 differentiation is observed, the anterior region being the one from 

 which pseudopodia are extended, the posterior, the part of the 

 body following and flowing into the advancing pseudopodia. 



Diatoms and other unicellular plants are the chief food of 

 Ainwba proteiis. Ingestion of solid food particles by their being 

 enclosed by pseudopodia and simply engulfed by the flowing pro- 

 toplasm may be a matter of common observation, but the causes 

 which underlie the process are not so clear. 



Relative adhesions between the food particle and the water in 

 which'it rests on the one hand and the food particle and the pro- 

 toplasm of the A))iu-ba on the other hand are probable factors in 

 the process^of ingestion, but it is to be remembered that Amceba 

 is a living cell, a cell in which chemical changes take place rap- 

 idly and choice of food exhibited by it, no doubt, depends upon 

 physiological states of its protoplasm. 



Although generally distributed and found almost everwhere 

 in both 'stagnant infusions and fresh water Amcvba protciis \s zx). 



[Proc. D. a. S., Vol. XI.] 2 [April 2S, 1906.J 



