lOo PROTOPLASM 



out in the pseudopodial threads indications of very delicate 

 expansions, which were occasionally distinctly composed of 

 a meshwork 



All these observations awaken the suspicion that the 

 ultimate nature of the darker pseudopodial threads, which 

 are only just visible, is not yet exhaustively made out, but 

 that they may yet possess extensions which are visible only 

 with the greatest difficulty. It is conceivable that the fine 

 pseudopodial threads really play the part of an axial thread, 

 such as occurs in the Heliozoa and to some extent also 

 in Eadiolaria, and that on this axial thread a thin and 

 scarcely visible coating of protoplasm is moving. Such an 

 idea obtains some additional support from the fact that 

 by rapidly kUling the Ehizopods with the vapour of osmic 

 acid,^ or some other quickly acting reagent, the pseudopodia 

 can only rarely be preserved quite intact. Usually they 

 assume a varicose nature, since numerous and closely con- 

 secutive spindle-shaped aggregations of protoplasm form 

 on them. These aggregations, which show the meshed 

 structure distinctly, and sometimes a marginal alveolar layer 

 as well, are connected with one another by a fine thread, which 

 is for the most part quite structureless. I also frequently 

 obtained preparations in which this thread could be followed 

 right through the swelling. The similarity is very great 

 between such appearances and those presented by the pseudo- 

 podia of Heliozoa after death, when the protoplasm on 

 the axial threads runs together into varicosities. Although 

 therefore I cannot, bring forward any certain proof of a 

 structure of this kind in the fine pseudopodia, nevertheless I 

 regard the hypothesis which I have suggested as worthy of 

 consideration. I only found out afterwards that M. Schultze 

 (1863) had already been led to the same supposition by 

 similar observations on the protoplasm of the Milwlidce. 



^ The pseudopodial networks were best obtained in a state of fixation by 

 the method of bringing the slide with the Rhizopod in a small drop of water 

 very quickly into a glass vessel, the air in which was richly impregnated with 

 osmic vapour by heating a 1 per cent solution on the water bath. As has been 

 said, the pseudopodial network can be preserved in its full development in 

 this manner, but rapid killing with fluid fixing agents under the cover glass 

 also frequently gives good working results. 



