Remarks

The above paragraphs give our findings on general procedural techniques for pre-embedding and embedding a specimen in plastic. Two other techniques, a direct result of trying to correct some of our failures, may be of interest. The first concerns the removal of large air bubbles and cracks both from within and outside the specimen in the fully hardened block. These defects we found could be removed by drilling holes along the course of the cracks, and/or into the air bubbles and then filling these page break

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Fig. 6 Chick embryo to show one method of storing embedded specimens in a plastic bag.
Fig. 7 Weta—Hemideina thoracia (Orthoptera).
Fig. 8 First embedded specimen of an alizarin preparation to show the skeleton of the flatfish Rhombosolea retiaria (alizarin preparation by J. Manikiam, Zoology Department, V.U.W.).
Fig. 9 Peripatoides novae-zealandiae (Onycophora).
Fig. 10 Cicada—Melampsalta muta (Homoptera).
Fig. 11 Hydrocoral.
Fig. 12 Enlarged view of Rhombosolea retiaria. ab = air bubbles.

page 7 with new catalyzed resin. But before the new filling is made, the drilled areas should be cleaned out with acetone. It is frequently difficult to detect "the fill" from the original block texture.

Secondly, we also found that hardened plastic blocks turned very well on the metal lathe. This allows sections to be made of the specimen at various levels and through a variety of planes. We have not as yet experienced any difficulty in keying on an entirely new surface to the block or filling the cavities made at various levels through the specimen. Cavities, however, need careful cleaning out with acetone, and acetone should be allowed to remain in the cavities for 2-3 hours before the new plastic is poured into them. The junction lines between the original hardened block and the newly made pour can usually be detected, but they do not as a rule impair viewing of the specimen under the binocular microscope.

Fig. 5 Linisher belt sander, showing modifications for polishing the fully hardened plastic blocks. A = vacuum tube; B = rubber suction cup of lever arm to hold block firmly but lightly on the belt.

Another method of making sections is to grind down the block on the sander using the coarse belt. This is a particularly useful technique for sections of hard material such as teeth, bone, or corals. The block is polished in the usual way and either resurfaced with a very thin layer of plastic, or the block is surface sprayed with plastic. If the latter method is used it is possible to protect the viewing surface of small blocks from scratches by lowering a glass coverslip on to it while the spray layer is still liquid. We have used this method with success for small blocks containing sectioned teeth.

Other devices we have employed for protecting small specimens, or groups of specimens such as a developmental series of chick embryos, is to embed and retain the hardened block in a petri dish. This ensures, for small blocks that will receive a great deal of handling, microscopic viewing surfaces that are relatively free from scratches, and provides also for more or less dust-free storage. Our larger blocks are stored in plastic bags (Fig. 6).

We have found plastic letters pressed on to the surface of the block very suitable for labelling museum and special demonstration specimens. After labelling, the page 8surface is sprayed with plastic. Thin card labels sealed at one end of the plastic bag (Fig. 6) provide a more rapid and economical method for labelling specimens for a large class.

The paragraph below, outlining the procedures for embedding a small wet-preserved, soft-bodied specimen is given as a summary of the major techniques described above.