108 THE MICROSCOPE AND ITS REVELATIONS. 



at the bottom of the vessel with comparatively little extraneous matter, 

 :after this operation has been repeated two or three times. It would 

 always be well to examine the first deposit let fall by the water that has 

 been poured-away; as this may contain the smaller and lighter forms of 

 Foraminifera. But supposing that it be only desired to obtain the dead 

 shells from a mass of sand brought-up by the dredge, a very different 

 method should be adopted; The whole mass should be exposed for 

 some hours to the heat of an oven, and be turned-over several times, 

 until it is found to have been thoroughly dried throughout; and then, 

 after being allowed to cool, it should be stirred in a large vessel of 

 water. The chambers of their shells being now occupied by air alone 

 (for the bodies of such as were alive will have shrunk-up almost to 

 nothing), the Foraminifera will be the lightest portion of the mass; and 

 they will be found floating on the water, while the particles of sand, etc., 

 subside. Another method, devised by Mr. Legg, consists in taking ad- 

 vantage of the relative sizes of different kinds of Foraminifera and of 

 the substances that accompany them. This, which is especially applica- 

 ble to the sand and rubbish obtainable from Sponges (which may be got 

 in large quantity from the sponge-merchants), consists in sifting the 

 whole aggregate through successive sieves of wire-gauze, commencing 

 with one of 10 wires to the inch, which will separate large extraneous par- 

 ticles, and proceeding to those of 20, 40, 70, and 100 wires to the inch, 

 each (especially that of 70) retaining a much larger proportion of Foram- 

 iniferal shells than of the accompanying particles; so that a large portion 

 of the extraneous matter being thus got rid of, the final selection becomes 

 comparatively easy. Certain forms of Foraminifera are found attached 

 to Shells, especially bivalves (such as the Chamacece) with foliated sur- 

 faces; and a careful examination of those of tropical seas, when brought 

 home ' in the rough,' is almost sure to yield most valuable results. The 

 final selection of specimens for mounting should always be made under 

 some appropriate form of Single Microscope ( 43-48); a fine camel- 

 hair pencil, with the point wetted between the lips, being the instrument 

 which may be most conveniently and safely employed, even for the most 

 delicate specimens. In mounting Foraminifera as Microscopic objects, 

 the method to be adopted must entirely depend upon whether they are 

 to be viewed by transmitted or by reflected light. In the former case it^ 

 should be mounted in Canada balsam ( 210); the various precautions to 

 prevent the retention of air-bubbles, which have been already described, 

 being carefully observed. In the latter no plan is so simple, easy, and 

 effectual, as the attaching them with a little gum to wooden slides (Fig. 

 124). They should be fixed in various positions, so as to present all the 

 different aspects of the shell, particular care being taken that its mouth 

 is clearly displayed; and this may often be most readily managed by at- 

 taching*the specimens sideways 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 (Fig. 95); whilst for the examination of 

 specimens in every variety of position, Mr. R. Beck's Disk-holder (Fig. 

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

 the several individuals differ considerably from one another, special care 

 should 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 Foraminifera, it will often 

 be necessary to make extremely thin sections, in the manner already de- 

 scribed ( 192-194); and much time will be saved by attaching a nunv 



