10;i The Miceoscope. 



" 200,000." These persons, however, admit, that the higher bands 

 furnish only passing glimpses, and cannot be kept in fociis and 

 examined at leisure or shown to other observers, as can be done with 

 more or less ease up to " 120,000." Is it possible, that, after looking 

 long and intently at the coarser and really visible lines, the retinal 

 impressions may remain and be recognized by the observer, while 

 subsequently gazing at the higher bands ? 



On another occasion, when it was claimed that all the bands of 

 a duplicate plate were resolved, and that the illumination was excep- 

 tionally good and the resolution exceptionally easy, the writer and 

 his two friends with younger eyes who accompanied him, recog- 

 nized the lines of the " 110,000" band very easily and distinctly, but 

 failed to go further. 



It would be evidently improper to undertake to anticipate the 

 action of the committee as a whole, by saying exactly what should 

 be sufficient evidence, to establish the reality of certain of the lines 

 and the fact of their resolution; but it will be noticed that the 

 projecting alternate lines must greatly aid in the task of counting a 

 measui-ed portion of a band, either with a micrometer or by aid of 

 photography. It can scarcely be long impossible to make a satisfac- 

 tory count of the band claiming to be spaced at " 120,000," if it is 

 correctly ruled, since the lines really to be counted are only at 

 "60,000." And if, which is not impossible, though not yet formally 

 demonstrated, this band should prove to be successfully ruled and to 

 be resolvable by existing lenses, a fact that has been plausibly claimed, 

 but never yet really proved of any band of equal fineness, then the 

 study of the next two bands would be one of the most interesting 

 problems in the practical optics of the present day. At the same 

 time it seems not improbable that photography may not only give us 

 an easy count of lines visible, but extremely difficult to count other- 

 wise, but may yet show the details of bands that are permanently 

 beyond the reach of direct microscopic vision. 



THE TAPE-WORM : METHODS OF PREPARATION. 



COOPER CURTIS. 



THE original investigations regarding the methods of prepara- 

 tion of the tape- worm for. the museum and the microscope 

 published in your issue for December, 1887, and presented before the 

 Pittsburg assemblage of the American Society of Microscopists, 1887, 

 have much of interest, and demonstrate the care and skill with which 



