in the Pseudopodia of the Rhizopoda. 413 



proach each other and cross at an acute angle, some of the fila- 

 ments are moved out of their place, and pushed together into 

 the angle so as to form an apparent plate. The extraordinary 

 flexibility of these filaments, and their great tendency to adhere 

 to each other, are properties which evidently assist in the forma- 

 tion of such membranes and plates. 



It is evident that the conditions for the displacement of the 

 simple filaments contained in two approximated pseudopodia so 

 as apparently to form membranous plates are not limited to the 

 crossing of such pseudopodia under an acute angle : two bundles 

 of pseudopodia merely touching each other with the vertices of 

 their curves, and then again separating a little, will also give rise 

 to the appearance of seemingly membranous plates ; and a case 

 has even occurred to me in which an apparently membranous 

 bridge-like union was formed at the spot where the separation 

 of two pseudopodia issuing from one bundle had not quite been 

 completed. 



After these explanations, I believe there will not be the least 

 difficulty in the comprehension of the multifarious changes of 

 form in the whole radiary complex of pseudopodia, in which, by 

 local contraction in any section, however small, of each filament, 

 innumerable moving particles may be represented. When the 

 animal extends its pseudopodia, the more simple radiate arrange- 

 ment predominates; soon afterwards the apparent ramifications 

 commence, and become constantly more numerous. The branches, 

 after issuing or being set free, easily reach neighbouring filaments, 

 apply themselves to these, and then appear as anastomoses. By 

 the multiplication of such apparent anastomoses, those reticulated 

 figures are produced which are known under the name of the 

 sarcode-net. At the same time, when the conditions are favour- 

 able, numerous membrane-like structures and bridge-like unions 

 between the filaments become visible. These are more widely 

 stretched the more numerous the filaments or the thicker the 

 bundles which touch each other at the part implicated, and, by 

 the imperceptible displacement of the finer filaments contained 

 in them, furnish a more abundant material for the formation of 

 the apparently membranous plates. The causes of the altera- 

 tions of form in the general radiary system of the pseudopodia 

 are to be sought chiefly in their movements, either active or 

 passive — i. e. produced by the ready adhesion of the filaments to 

 each other ; by these are effected the displacements of the innu- 

 merable particles in the general radiary system, which are often 

 imperceptible, and limited to the very smallest space. Favour- 

 able conditions for the multiplicity of forms, and for their ready 

 and often imperceptible change, are also furnished by the extra- 

 ordinary number of the filaments and their ready flexibility. 



