382 



GENERAL PHYSIOLOGY 



nounced phenomena of contraction, according to the very various 

 grades of irritability of the different species. 1 An Amceba or an 

 Adinosphcerium, stimulated in this way, ceases momentarily its 

 centrifugal protoplasmic streaming, i.e., the extension of its 

 pseudopodia; upon stronger stimulation there may be a partial 

 indrawing of the pseudopodia, a transitory centripetal streaming. 

 Other forms, such as Difflugia, react more energetically (Fig. 173). 

 With a gentle shock the pseudopodia become slowly more or less 

 retracted, their previously smooth contour becoming wrinkled 



FIG. ns.Difflugia. From the shell of sand-grains project three finger-like pseudopodia. 

 A, Unstimulated ; B, stimulated by a gentle shock. 



(Fig. 173, B ) ; with a stronger shock the pseudopodia are frequently 

 drawn with such force into the protoplasmic body, that their ends, 

 being fastened to the support by means of a sticky secretion, 

 are torn off. With stronger stimulation the change in the 

 pseudopodia is much more pronounced than with feebler : they 

 become not only wrinkled, but on their whole surface small drop- 

 lets swell out from the smooth contour ; 2 the more the reaction 

 develops, the larger become the droplets ; they flow together into 

 n myelin-like mass, and are distinguished clearly by a strongly 

 refractive strand visible in the axis of the pseudopodium (Fig. 174) ; 

 1 Of. Verworn ('89, 1). 2 C Fig . 156) p> 363- 



