in the Pseudopodia of the Rhizopoda. 409 



which occurs and advances upon the fihform contractile organ, 

 in the form either of a local thickening or of a local curvature 

 and loop-formation, can be referred to. 



The first question is, whether the described microscopic ap- 

 pearances suit with the assumption that the contraction-wave is 

 caused by local thickening of the filament suddenly occurring 

 at any point and then advancing further : the apparent granule 

 in the so-called granular movement would then have to be re- 

 garded as the thickened point. From a deficiency of observa- 

 tions, nothing can be said as to whether the apparent fusiform 

 thickening of the filament must necessarily precede the forma- 

 tion of a knot-like or grain-like swelling and agrees with the 

 preliminary assumption in regard to the contraction-wave. But 

 it may be affirmed that an advancing knot-like thickening of the 

 filament could not produce the microscopic appearance actually 

 seen — as if a granule advanced by jerks upon the surface. Nor 

 could the microscopical picture be produced even if the local 

 swelling of the filament on all sides were of considerable eleva- 

 tion, forming, as in the case of Astasia flavicans observed by 

 Ehrenberg, a circular disk, through the central point of which 

 the unchanged portion of the filament seemed to pass; for, 

 during the progress of such a swelling, the microscopic appear- 

 ance would be as if a ring were drawn along the filament. 

 There is only one case in which, in my opinion, the contraction- 

 wave in the form of an advancing local thickening could corre- 

 spond with the microscopic appearances described : the thicken- 

 ing must occur on one side, and in the form of a clubbed pro- 

 cess or appendage of the pseudopodium ; the club-shaped end 

 would then, as it advanced along the pseudopodium, be espe- 

 cially visible and indeed as an apparent grain, seeming to move 

 along on the surface of the filament. No such contraction-form 

 has, however, hitherto been observed ; and its assumption seems 

 to me rather bold. 



On the contrary, the granular movement seems to be easily 

 intelligible, and at the same time in perfect accordance with 

 other contraction-forms, both in its occurrence and disappear- 

 ance and in its progress, if we imagine that the contraction-wave 

 is formed by a loop advancing along the filament, produced in 

 consequence of contractile movements of the substance invisible 

 to us. With this supposition the microscopic appearances 

 during the production and, in reversed order, during the cessa- 

 tion of the granular movement especially correspond ; the loop, 

 when just rising, will be seen at first as an elongated swelling, 

 afterwards becoming thicker in the middle, and projecting be- 

 yond the level of the filament. The elevated loop will also, in 

 consequence of the refraction of the vertex of the curve, present 



