276 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



a cylindrogenic activity * is merely to play with useless terms. The 

 adherence of the body to the substratum which permits of the extrusion 

 of a pseudopodium does not necessarily require the extrusion of mucilage 2 , 

 and the retraction of the hinder pseudopodia during onward movement 

 merely involves the overcoming of the adhesion of the pseudopodium to 

 the substratum. It is, however, not impossible that the degree of adhesion 

 is capable of autogenic modification and that a mode of progression some- 

 what resembling that of the foot of a snail is involved. 



The movement is about as rapid as that of Diatoms and Oscillarias, 

 since under favourable circumstances it does not exceed 0-006 mm. per 

 second. Hofmeister 3 gives a velocity of 0-4 mm. per minute for Didymium 

 serpula, and one of 0-15 of a millimetre per minute for Stemonitis fusca. 

 In certain animals, however, the pseudopodia are rapidly protruded and 

 retracted. The fact that plasmodia may creep upwards over moist sub- 

 strata in air shows that the energy of movement is sufficient to support the 

 weight of the organism and even to raise a somewhat greater load. The 

 latter cannot, however, be very great owing to the feeble cohesion of 

 the protoplasm. Hence in soft gelatine locomotion is arrested, although 

 periodic attempts at amoeboid movement may be recognized 4 . Small 

 amoebae as well as leucocytes may, however, be able in virtue of their 

 plasticity to worm their way through minute pores, which they either find 

 at their disposal, or which they produce by a solvent action like that of 

 parasitic Fungi 5 . 



SECTION 61. The Mechanics of Amoeboid Movement. 



It was assumed by Mohl and Nageli that protoplasm has the 

 properties of a viscous fluid, and no doubt now exists that this is true 

 in the great majority of cases. The views of certain authors that proto- 

 plasm is a colloidal solid are incorrect, although naturally no hard and 

 fast boundary exists between such solids and viscous liquids 6 . Evidence 

 of the liquid nature of protoplasm is afforded by the spherical shape 

 assumed by isolated portions of protoplasm when suspended in a liquid 

 of the same density, as well as by the rounded shape of the vacuoles. The 

 existence of streaming movement 7 , the drawing out of the protoplasm 



1 Jensen, Die Protoplasmabewegung, 1902, p. 7. 



a De Bary, 1. c., p. 458 ; Rhumbler, 1. c., p. 158; Jensen, 1. c., p. 36. 



3 Hofmeister, Pflanzenzelle, 1867, p. 23. Cf. also Jensen, I.e., p. 15. 



* Pfeffer, 1. c., p. 277. On the work done by the pseudopodia of animals cf. Jensen, I.e., p. 14. 



5 On Plasmodiophora see Nawaschin, Flora, 1899, p. 404. 



8 Hofmeister, Pflanzenzelle, 1867, p. i ; Berthold, Protoplasmamechanik, 1886, p. 85; Pfeffer, 

 Zur Kenntniss d. Plasmahaut u. d. Vacuolen, 1890, p. 267; Biitschli, Unters. iiber mikroskop. 

 Schaume, 1902; Rhumbler, Archiv f. Entwickelungsmechanik, 1898, Bd. VII, p. 172; Zeitschrift f. 

 allgem. Physiologic, 1902, Bd. I, p. 279 ; 1903, Bd. n, p. 183. 



7 Ewart, Protoplasmic Streaming in Plants, 1903, p. 16. 



