i 3 4 THE MICROSCOPE. 



Visibility of Ruled Lines. — In an article in your issue of 

 May 5, on "The Visibility of Ruled Lines," there are some state- 

 ments which do not agree with my experience. I find that lines 

 properly ruled on glass are similar to graven lines; they are smooth, 

 clean cut, having a definite shape and depth. Such lines are always 

 visible in the microscope, and central or oblique light will show the 

 bottom of each cut as a dark or colored line, plainly visible, and re- 

 quiring no graphite or other foreign substance to indicate it. The 

 microscope is the test for a properly ruled line. The mechanical 

 elements (pressure, etc.) entering into the process of ruling are not 

 at all evidences that lines have been properly ruled. The slightest 

 accident to the point of the cutter, or the surface of the glass not 

 being perfectly clean, will spoil a line; that is, produce a scratch 

 which cannot be satisfactorily illuminated in any light. Well ruled 

 bands of lines, 70,000 or 80,000 to the inch, are visible in the micro- 

 scope with central light; and with a Smith vertical illuminator (giv- 

 ing central light). I have seen 100,000 lines to the inch. As these 

 individual lines have a width of about ^ Tro VuT of an mcn onl y> xt Io1 " 

 lows that the difficulty is not to see such a narrow line, but to elim- 

 inate the diffractions which tend to blur the image in the micro- 

 scope, and so prevent the resolution or separation of the lines in a 

 band of them. — C. Fasoldt, in Scientific American. 



Development of Volvox. — Miss S. G. Foulke presented a 

 communication upon the development of Volvox globator and its 

 separated gonidia or reproductive spores. It was stated that in one 

 case some of the gonidia freed themselves from the protoplasmic 

 envelope, breaking the connecting filaments, and swam away. In 

 some instances these free gonidia passed into an encysted state; 

 in others, attached themselves by the remains of the fdament to 

 other substances, thus using it as a footstalk, and presented the 

 appearance of Vorticella. Many of the free gonidia remained in a 

 free swimming state. Others remained in the Volvox, developed in 

 Amoebae, and emerged, after enveloping and digesting some of the 

 neighboring gonidia. These Amoebae afterwards took the form of 

 Amoeba radiosa, and then returned to their former state, seeming 

 to have the power of using either shape at pleasure. As the parent 

 Volvox belongs to the microscopic Algae, or water-plants, the 

 change of its spores to a form in all respects apparently identical 



