DIFFICULTIES OF THE THEORY 315 



quite natural, inasmuch as the internal protoplasm, which is 

 subject to the action of the enchylema, is quite fluid, for 

 which reason it does not seem an unwarrantable assumption 

 that the viscid external layer would also become liquefied 

 again if it was temporarily removed from the influence of 

 the water by a spreading out of enchylema on its outer 

 surface. 



If, as I think, we have found in this interpretation of 

 amoeboid movement an explanation which is both very 

 probable and harmonises well with the observations upon the 

 froth-drops, it should nevertheless not be ignored that the 

 same explanation cannot be applied off-hand with good 

 results to fine reticulose pseudopodia. It is, of course, 

 quite conceivable that here also thicker pseudopodia may 

 possibly develop in the way described, but on the other 

 hand I willingly admit that the explanation of filament- 

 ous pseudopodia, frequently of excessive fineness, cannot 

 be reached in this way. It is sufficiently obvious, from 

 the description which has been given before, that in these 

 pseudopodia other and special relations come into the 

 problem, which are not as yet satisfactorily cleared up. 

 I refer in this respect more especially to the behaviour of 

 the long filamentous pseudopodia during their retraction. 

 It is well known that during this process they for the most 

 part become suddenly relaxed in a peculiar manner, and 

 even occasionally assume a zigzag or spiral form. Although 

 we are not able to explain this peculiarity off-hand, it may 

 be taken, as has been said, as a proof of the fact that there 

 are here other peculiar conditions lying at the root of the 

 matter. 



It has already been shown above that Berthold's 

 attempt at an explanation of these fine pseudopodia, 

 which are also frequently raised up free in the sur- 

 rounding medium, is in no way satisfactory. Just as little 

 satisfactory is the explanation given by Quincke. The latter 

 seeks to refer the origin of pseudopodium-like bridges and 

 threads of protoplasm, such as so frequently traverse the 

 cell sap of plant cells, to the formation of firm threads of 

 albumen at the boundary between his protoplasmic utricle 



