The use of a Chinese ink suspension to provide a background against which will be revealed the thickness of transparent jelly-layers, etc. The membranes, only, of certain other eggs will absorb the dye, and there are also cases where both the jelly and the membranes are stained. For true intra vitam staining with Janus green, however, a zinc-free preparation must be obtained. It is essential that the glassware used for living material be completely free of all toxic substances. He has given excellent advice, also, on utilization of sea water, and on the uses of thermometers and stop-watches in embryological research.
Some workers prefer a paraffin coated low hardware-cloth rack to the round glass platform.
The experimental embryologist who works with marine material makes use of many of the instruments originally devised for operative techniques in vertebrate experimental embryology. Another most useful implement for moving eggs without injury from one container to another is the mouth pipette. Wooden blocks about two inches in thickness, with a series of holes drilled in them, are useful as racks for glass needles, hair loops, etc. They should be provided with glass or rigid plastic bell-jar covers. Since most of the marine invertebrate eggs are very much smaller than the traditional amphibian and chick material, the hair loops should be smaller in diameter and made of finer hair than those used by the worker with vertebrate eggs and embryos.