466 



ZOOPHYTES. 



dilute to be destitute of any injurious action on the cement. 

 Q-oadby's fluid also may be used ; but the preservation of the 



soft parts is not quite so 

 Fig. 224. Complete with it as with 



spirit. The size of the cell 

 must of course be propor- 

 tioned to that of the object; 

 and if it be desired to mount 

 such a specimen as may serve 

 for a characteristic illustra- 

 tion of the mode of growth 

 of the species it represents, 

 the large shallow cells, whose 

 walls are made by cement- 

 ing four strips of glass to the 

 plate that forms the bottom 

 (§ 136), will generally be 

 found preferable. The horny 

 polyparies of the Sertularidse, 

 when mounted in Canada 

 balsam, are beautiful objects 

 for the Polariscope ; but in 

 order to prepare them suc- 

 cessfully, some nicety of ma- 

 nagement is required. The 

 following are the outlines of 

 the method recommended 

 by Dr. Golding Bird, who 

 very successfully practised it. The specimens selected, which 

 should not exceed two inches in length, are first to be submitted, 

 while immersed in water of 120°, to the vacuum of an air-pump. 

 The ebullition which will take place within the cavities, will 

 have the effect of freeing the polyparies from dead polypes and 

 other animal matter ; and this cleansing process should be re- 

 peated several times. The specimens are then to be dried, by 

 first draining them for a few seconds on bibulous paper, and then 

 by submitting them to the vacuum of an air-pump, within a thick 

 earthenware ointment pot fitted with a cover, which has been 

 previously heated to about 200° ; by this means, the specimens 

 are very quickly and completely dried, the water being evapo- 

 rated so quickly that the cells and tubes hardly coflapse or 

 wrinkle. The specimens are then to be placed in eamphine, and 

 again subjected to the exhausting process, for the displacement 

 of the air by that liquid; and when they have been thoroughly 

 saturated, they should be mounted in Canada balsam in the usual 

 mode." When thus prepared, they become very beautiful trans- 

 parent objects for low magnifying powers; and they present a 

 gorgeous display of colors when examined by polarized light, 

 with the interposition of a plate of selenite. These objects are 



Sertvlaria cupressina:—A, natural size; 

 magnified. 



porlion 



