in the Pseudopodia of the Rhizopoda. 41 1 



applied to each other entirely or partially m the direction of 

 their length. The united filaments, except when very thick 

 bundles come together, do not appear thicker than the 

 separate ones ; if one of the filaments be shorter than the 

 other, the point at which it terminates is not perceived. From 

 this it follows, as already observed, that we can never say with 

 certainty that any filament is simple. Further, the united fila- 

 ments, in consequence of active movement in one or both of 

 them, may separate again partly or entirely. By this means an 

 orifice may occur in the united filaments, which closes again in a 

 state of repose ; or only the apex of one filament separates from 

 the other, and the united, apparently simple, filament then 

 possesses a branch, and appears branched. My attention having 

 been attracted to this, I could not but ask myself the question, 

 whether the ramifications are not throughout only apparent. 

 From my investigations, this question must be answered in the 

 affirmative. I have met with no case of ramification which 

 could not have been explained in the most natural manner by 

 the protrusion of the extremities of filaments from an apparently 

 simple pseudopodium ; nay, the usually sudden shooting forth of 

 such branches is not in favour of their production being effected 

 by movements of contraction. 



In two filaments crossing each other at an acute angle, an 

 appearance is observable upon which, as a proof of the coalescence 

 of the pseudopodia, great stress has been laid, especially by 

 Dujardin ; the angle is very frequently seen to be occupied by a 

 web-like structure. When the angle is very acute, and the ap- 

 pearance not much diffused, the suspicion that there is some 

 optical illusion cannot be altogether got rid of; in other cases 

 it is seen quite distinctly that the angle formed by the two fila- 

 ments is occupied by a hyaline or generally finely granular sub- 

 stance. The comparison with a swimming membrane is, however, 

 not quite suitable ; for no filament is to be distinguished on the 

 margins or in the region of the apparently membranous struc- 

 ture. From the microscopic appearance, it might equally well 

 be said to be a triangular plate from the angles of which fila- 

 ments issue. 



I will not deny that such a web-like structure may be pro- 

 duced by the overflow of the mass of two fluid filaments ap- 

 proaching each other at an acute angle. But in the present 

 case, taking into consideration our previous knowledge of the 

 morphological conditions of the organization of animals, in order 

 to show that they make their appearance by such a mode of pro- 

 duction it must first of all be proved that the filaments consist 

 of a fluid substance ; or, if the web-like plate itself is to serve as 

 evidence of the fluid consistence of the pseudopodia, it would 



