MOUNTING FORAMINIFEnA. POLTCTSTINA. 523 



Mouth is clearly displayed; and this may often be most readily 

 managed by attaching the specimens sidexcays to the wall of the 

 circular depression of the Slide. Or the specimens may be 

 attached to Disks fitted for being held in Morris's Disk-Holder 

 (§ 95); whilst, for the examination of specimens in every variety 

 of position, Mr. R. Beck's 'Revolving Disk-Holder' (Fig. 76) will 

 be found extremely convenient. Where, as will often happen, 

 the several individuals differ considerably from one another, special 

 care shoidd be taken to arrange them in Series illustrative of their 

 Range of Variation and of the mutual connections of even the most 

 diverse forms. — For the display of the Internal Structure of Fora- 

 minifera, it will often be necessary to make extremely Thin Sec- 

 tions, in the manner already described (§§ 138-140) ; and much 

 time will be saved by attaching a number of specimens to the 

 Glass-slide at once, and by grinding them down together. For 

 the preparation of Sections, however, of the extreme thinness that 

 is often required, those which have been thus reduced should be 

 transferred to separate slides, and finished-off each one by itself. 



402. Polyctstina. — These are minute Siliceous shells, possessing 

 wonderful beauty and variety of form and structure, which contain 

 in the living state an olive-brown ' sarcode,' that extends itself into 

 pseudopodial prolongations (resembling those of the Actinophrys, 

 § 329), which pass through the large apertures by which the shells 

 are perforated (Plate xviii., figs. 3, 4). The sarcode-body does not 

 always fill the shell ; often occupying only its upper part or vault, 

 and showing. a regular division into four lobes. The Shells are 

 in some instances most perfect spheres (Plate xix., fig. 1) ; and 

 occasionally we find a whole series of such spheres arranged con- 

 centrically one within another, and connected by radiating rods 

 (fig. 2). They are often prolonged into spines or other pro- 

 jections, which sometimes branch in a very remarkable manner 

 (figs. 4, 5). It seems probable that these creatures are almost 

 as widely diffused at the present time as are the Foraminifera, 

 although from their greater minuteness they have not been so often 

 recognized. For having been first discovered by Prof. Ehrenberg 

 at Cuxhaven on the North Sea, they were afterwards found by him 

 in collections made in the Antarctic Seas, and have been described 

 by Prof. Bailey as presenting themselves (with Foraminifera and 

 Diatomaceas) in the deposits brought-up by the sounding-lead from 

 the bottom of the Atlantic, at depths of from 1 000 to 2000 fathoms. 

 They have also been studied by Prof. Muller* in the Mediter- 

 ranean ; and an immense variety of forms occurring in the Adriatic 

 has been described in the magnificent work of Prof. Haeckel ;+ 



* ' TTber die Thallassicollen, Polycystinen, und Acanthometren des Mit- 

 telraeeres,' in " Abhandlungen der Konigl. Akad. der Wissensch. zu 

 Berlin," 1858, and separately published ; also ' Ueber die im Hafen von 

 Messina beobachteten Polycystinen,' in the " Monatsberichte " of the 

 Berlin Academy for 1855, pp. 671-676. 



t " Die Radiolarien (Rhizopoda Radiaria)," Berlin, 1862. 



