TECHNIQUES 351 



Stage I and even occasionally at stage 2 resorbed the primordium 

 if they were kept too long in the viscous fluid, and regenerators 

 either did likewise or the anlage was considerably delayed in its 

 appearance. After cutting in methyl cellulose the animals should 

 therefore be washed once by passing them through a large drop of 

 filtered culture medium. Old solutions had a greater inhibiting 

 effect so that it is well not to employ dissolved methyl cellulose 

 which has been kept longer than two months. A stock solution of 

 methyl cellulose may be prepared in the following manner: add 

 50 ml of dry methyl cellulose to the same amount of boiling 

 filtered lake water used in culturing; stir the fibers to remove air 

 bubbles and assure complete wetting ; remove the beaker from the 

 stove and allow it to stand for half an hour, after which another 

 50ml of cool lake water is added with stirring; let stand overnight 

 until the solution is cool and the methyl cellulose thoroughly 

 dissolved. 



My method of operating is quite simple. I use a stereomicroscope 

 without base or mirror, because the instrument then stands low 

 and the bench itself can be used to give support to the arms 

 during deHcate operations with the needle (Fig. 97B). The 'scope 

 should have the highest powers available (about 150 x), which 

 still gives sufficient working distance between the lower lens and 

 the specimen to permit operating. Lower magnifications are needed 

 for capturing specimens. Sub-stage illumination is provided by a 

 hole in the bench covered by a heat filter glass with the light 

 underneath. But for operating, reflected light is used from an 

 embryological lamp, also supplied with a heat filter. It is con- 

 venient as well as saving of bulbs to arrange a pressure switch with 

 a strap hinge at the edge of the bench so that this light turns on 

 only when one bends over the microscope. Reflected light has the 

 great advantages of not silhouetting the stentor but clearly revealing 

 its entire surface topography, and of avoiding eye-fatiguing glare. 



Using a toothpick dip, a fairly large drop of methyl cellulose 

 solution is placed in the center of a piece of finely woven cloth 

 stuck with melted paraffin to a thick slide. The slight roughness 

 of the cloth keeps the specimen from skidding under the needle, 

 as it would on glass, thus helping to hold the animal in place. 

 Paraffining prevents spreading of the drop. A white cloth is used 

 for pigmented forms like coeruleus and a black cloth for unpig- 



