416 University of California Publications in Zoology [Vol. 19 



above (p. 415) illustrate four forms of shanks which were found most 

 serviceable. For convenience I have named these: a, right angled; b, 

 acute angled; c, obtuse angled, and d, V-shaped shanks. Needles a 

 and b have been used for probing or tearing regions or dissecting off 

 parts; needles c and d for making incisions and, particularly d, for 

 bisecting the organism, making wide incisions or snipping off organ- 

 elles. The V-shaped shank affords more flexibility, which may be 

 increased by lengthening the V. 



Control. — To provide for the control of the organism during opera- 

 tion, several methods were tried. Fine fibers of silk and of cotton, 

 also very finely ground particles of glass were sealed with agar to the 

 surface of the cover-slip. These afford helpful means of holding the 

 animal in place for the beginner until he has learned the rather diffi- 

 cult but by far the most satisfactory method of control, namely, water- 

 glass surface tension, suggested by Kite (1913, p. 146). I have used 

 a very small pipette with a rubber tube attached for the mouth as a 

 means of transferring the animals and reducing the volume of the 

 hanging drop to afford just the necessary amount of surface tension. 

 This amount one learns only after considerable practice. Allowing 

 slight degrees of evaporation also facilitated this proper adjustment. 

 The animal must be held in place but a further increase in surface 

 tension may cause it to disintegrate, often with explosive violence. A 

 perfectly clean surface of the cover-slip and a wide hanging drop, 

 say 10 mm. in diameter, aid greatly in obtaining proper surface ten- 

 sion. Another fairly satisfactory and more simple method of control 

 is to confine the protozoan within a very small hanging drop, the 

 surface tension of which with the glass is greatly reduced by applying 

 a mere trace of paraffin or some other harmless oil. 



In making an incision, the needle was applied suddenly and rather 

 firmly by means of the up-and-down movement screw. After an 

 interval of a few seconds, this screw was slowly turned back and forth, 

 which caused a seesaw movement of the needle-point. With proper 

 care and if the needle be not too flexible, a surprisingly clean cut may 

 thus be made without any loss of endoplasm. Chambers (1917a) has 

 very helpfully suggested the use of a needle not exceedingly fine and 

 the importance of slow movement and sufficient time in making an 

 incision. Otherwise a loss of endoplasm usually results and this may 

 be followed by rapid and complete disintegration. This outflow of 

 endoplasm may, however, be regulated to advantage by applying a 

 V-shaped needle near an animal in which a careful incision has been 



