OF THE PROTOZOA.-— EHIZOPOD A. 205 



of a contained softer matter or of grannies takes place, but each segment con- 

 tracts on itself and continues to live, and, again, that when a Rhizopod is 

 shaken about, its processes become flexuous, and float loosely instead of being 

 vvithdi'avvn within the general mass, as should happen if a general contractile 

 integument enveloped it. Among the Amabel generally, a distinct hyaline 

 cortical substance is found enveloping the interior more fluid matters, and 

 restraining their escape. (See afterwards, on shells of MonotliaJamia, excep- 

 tional forms noticed by Dujardin and Bailey, and the researches of Auerbach.) 



Although an integument be, therefore, no part of the structui^e of Rhizopoda, 

 yet their soft substance is capable, as is shown best in the Amoeb'ina, of resist- 

 ing internal pressure, such as that from silicious shells of DiatomecB and other 

 hard substances, which oftentimes cause irregular and sharp projections during 

 the movements of the animals, but yet very rarely perforate them. On the 

 other hand, Rhizopoda become sometimes impaled upon the rigid fibres of 

 plants or other substances, and, though thus transfixed, will move fi'om one 

 extremity to the other, without any apparent inconvenience or injury. This 

 cii'cumstance has been long noticed in the case of the Amoehce ; and Schultze 

 has figured a specimen of a testaceous Rliizopod — the Gromia Dujcuxlinii 

 — penetrated by a large curved hair. 



Dr. Auerbach, in a recent Essay on the AmoehaKi {Zeitsclir. 1855, pp. 365- 

 430), has advanced the statement, from observation, that all the Amcebce are 

 enclosed by an adhesive, elastic and structureless membrane or integument. 

 This fact has, he says, been so universally overlooked by reason of the diffi- 

 culty in determining it, and, where caught sight of, has been misinter- 

 preted, as, for instance, by Schneider {Midler's Arcliiv, 1854, p. 201), who 

 represents Amoeba enclosed by a membrane as being in a state of " rest," or 

 encysted. 



Auerbach makes particular reference to two new species discovered by him, 

 as illustrative of the presence of an integument, ^dz. A. bilimbosa (XXII. 7- 

 11), and A. act'mojyliora (XXII. 13), in both of which he detected a double 

 peripheral line. But besides this e\idence he appeals to the eff'ects of reagents, 

 of acetic or of diluted sulphuric acid and alkahne solutions, both on the species 

 just cited and on others well known — for instance, A. iirinceps — in demon- 

 strating the membranous investment. And what seems at least very strange, 

 we might say quite inexplicable, he asserts that upon all the processes, how- 

 ever branched, anastomotic, or fine, this membrane is extended to their very 

 extremities ; for on adding a dilute alkaline solution to Amoeba radiosa, the 

 granidar and molecular contained mass became shrunken, and retreated to- 

 wards the centre, leaving the figm^e of the animalcule with all its processes 

 as before the addition, the latter appearing as tubules mth closed ends, which 

 ruptured by over- extension. 



This same author accoimts for the entrance of solid particles from without 

 by imagining the integument to rupture to receive them, and then to close on 

 them so as to leave no trace of the proceeding. Fui^ther, the membrane is 

 not soluble, at the ordinary temperature, in acetic nor in mineral acids, nor 

 in dilute alkaline solutions, and therein agrees with the tissue noticed by 

 Cohn in Paramecium and other Ciliata {vide chap, on Ciliata), and with the 

 cell-membrane of animal cells. 



These observations of Dr. Auerbach are well deserving attention, although 

 we are indisposed to accept them in their entirety. The wonderful poly- 

 morphism, the coalescence of processes, and the particulars alluded to above 

 (p. 204) as inconsistent with the presence of an integument need not be 

 again adduced in argument. What is desirable is, that observations should 

 be multiplied on this subject, which is one that strongly commends itself to 



