OF THE PROTOZOA. KHIZOPOBA. 223 



marginal pores), the segments of the concentric zones are elongated into 

 vertical columns, with imperfect constrictions at inter^-als ; instead of a single 

 annular stolon, there are two, one at either end of these columns, between 

 which, moreover, there are usually other lateral communications, whilst the 

 radiating peduncles, which connect one zone with another, are also multiplied, 

 so as to lie in several planes. Moreover, between each annular stolon and 

 the neighbouiing surface of the disk, there is a layer of superficial segments 

 distinct from the vertical columns, but connected ^ith the annular stolons ; 

 these occupy the narrow elongated cells just mentioned, which constitute 

 two superficial layers in the disks of this type, between which is the inter- 

 mediate layer occupied by the columnar segments. 



'' These two types seem to be so completely dissimilar, that they could 

 scarcely have been supposed to belong to the same species ; but the examina- 

 tion of a large number of specimens shows that, although one is often 

 developed to a considerable size upon the simple type, whilst another com- 

 mences even from the centre upon the complex type yet many individuals, 

 which begin life and form an indefinite number of annuli upon the simple type, 

 then take on the more complex mode of development." 



Each cell is occupied by the animal sarcode substance — sometimes not 

 completely, so that intervals exist at points between the contained matter 

 and the enclosing calcareous wall, just as in Monothalamia. The first cell pro- 

 duced, about which all others are arranged and may be considered ofi'shoots 

 or dependencies, is called the primary or primordial cell ; and in it is con- 

 tained the mass of condensed sarcode which Dr. Carpenter calls the nucleus. 



The link-like portions connecting one chamber with another are called by 

 Schultze bridges (Briicken) or isthmi, by Ehrenberg siphons, and by Car- 

 penter ' stolons.' 



In chemical composition the shells of Poh/thalamia are calcareous, with the 

 exception of those of Polymorphina silicea, which, like those of many Diffiugice, 

 are composed of small granules and tablets of silex. Schultze observes that, 

 in addition to this species, Spiridina agglutinans and Bignerhia aggJutmans 

 have their surface covered by adherent grains of sand, to give it the fii'mness 

 and resistance provided for in other forms by theii' shells. The consequence 

 of their calcareous composition is, that the shells are hard, brittle, and opaque, 

 and their contents only visible so far as protruded in the form of processes. 

 To examine, therefore, the animal matter, it is necessary to crush the shells, 

 or, better, to carefully remove some portions and so expose the subjacent tissue 

 to view ; or they may be acted on by dilute acid, which dissolves out the 

 earthy matter, leaving the transparent organic basis of the testa. Dujardin 

 employed dilute acid mixed -^ith alcohol, which contracted and rendered 

 the sarcode substance harder, and gave it the appearance, in the many- 

 chambered cells, of laminated or lobulated masses connected together by 

 thinner portions. 



When the calcareous earthy matter is dissolved out of the shells oiForami- 

 nifera, the organic matrix or basis is left as a transparent membrane, retaining 

 the precise form and markings of the complete shell, and perforated by the 

 characteristic pores. Its chemical relations are those of the membranous testa 

 of Gromia. In thin shells the organic matter is in relatively greater abund- 

 ance than in the thick ones. Acids produce an active effeiTescence, and so 

 prove the presence of carbonate of lime as the principal mineral constituent. 

 Schultze has also detected the presence of phosphate of lime, at least in some 

 shells, viz. in those of Orbiculina adunca and PohjstomeUa strigilata. 



The shells of Polythalamia are commonly white, when viewed by reflected 

 light, and when emptied of their organic contents. \\Tien the latter remain 



