220 GENEEAL HISTOKY OF THE INFrSOEIA. 



in the solution of which chitine itself is dissolved. Further the shell is dis- 

 solved in sulphuric acid, and, unlike cellulose, is not coloured blue by this acid. 

 Such are the chemical relations of the testa of Gromia according to Schultze ; 

 and such we may presume with him are those of the freshwater genera 

 ArceUa, Eugli/jpha, and Trinema. 



The shells of Difflugia are peculiar by being composed in many species of 

 a softer substance, to which various foreign particles, shells oiDiatomece, grains 

 of sand and the like, adhere and thereby furnish an accidental or supple- 

 mentary shield to the animals (XXI. 17). The substance on which those 

 accidental matters are affixed we may presume to be chitinous, but not con- 

 densed or hardened as in the tnie testaceous forms. Schultze is disposed to 

 think that, besides merely agglutinated sihcious particles accidentally, as it 

 were, appropriated, the investing tunic has actually the power of secreting 

 sihcious molecules, represented by the smallest and most intimately adherent 

 granules of the testa. He would also extend this hy[3othesis to the sihcious 

 polythalamous shells, illustrated by Polymorpliina silicea (XXI. 38) and 

 another newly- discovered species. 



Cohn apparently saw young Difflugice in the act of building their sheUs. 

 These yoimg beings consisted of a mass of sarcode siuTounded by a muco- 

 gelatinous envelope, through which fibres were protruded in different dii*ec- 

 tions. These processes, by retraction, brought to the surface of the animal 

 various foreign particles, which had become affixed to them, and were then 

 imbedded in the mucous involucre. At length all other pseudopodes, save 

 those from one extremity, were permanently withdrawn, and the exterior of 

 the animal was clothed with a layer of silicious particles, grains of sand, shells 

 of Cyclotella, and of other Diatomece, many of them of a blackish or brown 

 colour'. 



Dr. Bailey indicates an exceptional tunic in a Rhizopod, having much of an 

 AmoehaA^kQ character, which he names Pamphagus. It would seem to be 

 enveloped by an integument, which, although resistant, admits of an immense 

 modification of figure, both from external and internal pressure, and ofi'ers no 

 impediment to the animal transfixing itself, just as if it were a completely 

 homogeneous jelly. ''These creatures," says their discoverer, " connect the 

 genus Amceba with Diffugia, agreeing with the first in the soft body without 

 shell, but difi'ering in having true feelers or rhizopods confined to the interior 

 part of the body." Just as in Difflugia, they are limited to the region of 

 the mouth. From this last-named genus, " and from the whole family of 

 Arcellina, these forms are distinguishable by having no lorica or shell." A 

 very similar tunicated amoebiform animal is described by Dujardin under the 

 name Corycia {A. S. N. 1852), which, although clothed by a membranous 

 envelope, can be twisted and folded in every direction by the movements and 

 contractions of the animal, and permits the extrusion of processes from any 

 part of its surface. In this respect it differs from the Parnpliagus of Bailey, 

 and certainly exemplifies a pecuhar phenomenon, which, in the case of the 

 usual variable processes mth circulating contents, would not be conceivable, 

 but become so upon the explanation of Dujardin, that they do not contract 

 on adhesion to the surface on which the animal moves, nor ghde along it in 

 the ordinary manner, but remain free, and, as we are told, seem only to serve 

 to change the centre of gravity of the animal. ^' It must, therefore," says its 

 describer, " form a new genus of Amoehina/^ intermediate between the naked 

 Amcebce and the Arcellina ; and in another direction indicating an aUiance 

 Avith the Noctilucida. 



With reference to these pecuhar beings, it is worth while to bear in mind 

 the account given by Cohn of the development of young Difflugice and the 



