6 BASIC METHODS FOR EXPERIMENTS 



Frequently, a water immersion lens could with profit be 

 used instead of an oil immersion. I have seen an experienced 

 worker make observations on living Amoeba proteus and A. dubia 

 under a 2 mm. apochromatic oil immersion lens of numerical 

 aperture, 1.4. No such observation has value for, since these 

 large protozoa are under great pressure, their behavior can not 

 be normal. A 2.5 mm. water immersion lens with numerical 

 aperture 1.25 would be more useful in such cases. 



Other Accessories 



A good stop-watch is indispensable for experiments that run 

 for seconds only and for timing changes that endure for frac- 

 tions of a second. When, as is often necessary, two stop- 

 watches are demanded, they should be as closely synchronized 

 as possible. I frequently use also an electric timing device. 

 This need not be expensive for several reliable makes are now 

 available at low cost. 



Bolting-silk with mesh of various sizes is most useful. As 

 shown beyond I use it for various purposes. Cheese-cloth, 

 scrim, gauze and "bird's eye" cloth should be at hand; the 

 first three named for straining eggs, the last named for cleaning 

 slides and cover-slips. Lens paper is useful for experiments on 

 the effects of pressure on eggs. 



Literature 



Just, E. E. 1915a. The morphology of normal fertilization in Platy- 

 nereis megalops. Journ. Morph., Vol. 26. 



'■ . 1915^. An experimental analysis of fertilization in Platy- 



nereis megalops. Biol. Bull., Vol. 28. 



. 1928. Initiation of development in the egg of Arbacia. 



V. The effect of slowly evaporating sea-water and its significance 

 for the theory of auto-parthenogenesis. Biol. Bull., Vol. 55. 



• . 1929. The production of filaments by echinoderm ova as a 



response to insemination, with special reference to the phenomena 

 as exhibited by ova of the genus Asterias. Biol. Bull., Vol. 57. 



