382 



GENERAL PHYSIOLOGY 



nounced phenomena of contraction, according to the very various 

 grades of irritability of the different species.^ An Amosba 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 



Via. 173.— D. 



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

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



(Fig. 173, i? ) ; 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 : thej' 

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

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

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

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

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



1 Cf. Verworn ('89, 1). ^ Qf j'jg. i^q p 363, 



