204 GENEEAL HISTORY OF THE INFUSORIA. 



than in another, or in all directions together ; and acciiraulations of their 

 mucous substance, or fusions, may take jjlace on any one side. In this family 

 the fiHform fibres are, as a rule, not seen protruded at any one time through 

 all the pores perforating the shells. 



Many genera have, besides the generally- distributed small foramina, a larger 

 orifice in the ultimate chamber ; such is seen in Botalia and Textilaria. In 

 these, says Schultze, it may be remarked that the jDi'ocesses fii'st throAvn out 

 come principally from the large openings, and frequently a considerable time 

 elapses before the numerous fine pores give exit to fibres. Often, again, the 

 filaments are extended only from the two or three last-formed cells. Yet 

 after long lying imdistiu-bed, fibres may be seen proceeding from eveiy part 

 of the surface of the finely porous shells. Still the question requires further 

 examination, to decide whether the processes can be extruded through all the 

 foramina or only thi'ough some of them in certain places. However, as 

 Schultze remarks, the universal porosity would seem without a purpose if it 

 does not give vent to the contained substance at all points. 



The processes of PoJytliaJamia attain the greatest length and fineness, and 

 often constitute a network of several hues in diameter, — the shell of the ani- 

 mal occupying the centre, like a sj^ider lodged in the middle of its web. The 

 length of such fibres not imcommonly exceeds twelve times the diameter of 

 the shell. The processes of most Monotludamia are not so numerous, and do 

 not equal on an average those of the Pol y thai cmiia, whilst those of the Amoebce 

 are mostly shorter and broader. The length, number, and fineness of the 

 processes, together with theii' mode of termination, supply, under considera- 

 ble hmitations, characters for distinguishing species chiefly of the Amcebina, 

 and, in a less degree, of the single- chambered testaceous Rhizopoda. 



The ever-fluctuating form of the animal mass and of its processes is ex- 

 pressed by the term "■ ijolymorphism,'''' It is, as before noticed, a well-marked 

 character of Bhizoj^oda, although not restricted to them ; for the like is exhi- 

 bited by the yolk-cells of Planaria, and by detached fragments of the substance 

 of Hydra ; in fact, illustrations are not wanting in the vegetable kingdom. 



The phoenomenon of polymorphism would seem to discountenance the hy- 

 pothesis of the presence of a limiting membrane or skin. Ehrenberg described 

 a resistant, very elastic, and contractile integument, and, to explain the vaii- 

 abihty of figure and the extension of the pseudopodes, supposed a relaxation 

 or suspension of the natm^al contractility of the integ-ument at the extending 

 point, and a consequent passive yielding before a pressure from within exerted 

 by the contained substance. This explanation he endeavoured to illustrate 

 by comparing the process with the formation of a hernia or rupture, — a com- 

 parison, by the way, involving an effort of imagination to discover any simi- 

 larity between the two occurrences. Thus he remarks of Aiyioeha princeps 

 that " its normal shape, if such it can be said to possess, is globular ; but it 

 can relax any portion of its body, and contract the rest, so as to force the in- 

 ternal substance do'wn into this relaxed portion, which thus becomes, as it 

 were, a hernial tumour." This notion is opposed by the results of observa- 

 tion. The very characters of the processes, their great length and frequent 

 tenuity, their branching, adhesion, and coalescence contradict the assimip- 

 tion ; and the fact of their not uncommon extensoin from all sides of an ani- 

 mal involves, as a consequence of Ehrenberg' s hypothesis, a behef in the 

 exertion of internal pressure in opposite dii-ections at the same time. Other 

 evidence of the error of this h5q)othesis is found in the following facts, ^dz. 

 the adhesion and entrance of foreign bodies at any part of the sarcode sub- 

 stance, the cohesion of two individuals, and that, as pointed out by Dujardin, 

 when the gelatinous mass of an Amoeba is torn or cut across, no escape 



