( 159 ) 

 NOTES AND MEMOEANDA. 



Resolution of Amphipleura pellucida by the 5^ of Mr. ToUes.— 



The ' Amoricau Naturalist' for July, 1874, contaius a note by Mr. 

 G. W. Morehouse on the above subject. A -^^j objective was made for 

 him by Tolles, and finished on the 12th of March, 1873. The angle 

 of aperture as invoiced by Mr, Stodder is 165^, From his own 

 measurements he thinks the objective is correctly named by the 

 maker. At the extreme open point it is a good 4^(5 th dry. The 

 screw-collar has twelve divisions ; by turning it eight divisions it is 

 adjusted for uncovered wet, and four divisions remain to adjust for 

 cover for immersion work. It works through covering glass of about 

 20^oth of an inch, but it is better to use thinner glass, or mica, to 

 enable the observer to focus through sijecimcns. With lamplight 

 and the 30th the resolution of Ampliijjleura pellucida is better than he 

 has before seen. Using ordinary daylight, vibriones, bacteria, &c,, 

 are well defined, especially when a Kelner eye-piece is used as a 

 condenser. With sunlight and the ammonia-sulphate of copper cell, 

 Surirella gemma yields longitudinal strias, and, as the direction of the 

 light is changed, rows of " hemispherical bosses " as described by Dr. 

 Woodward. With the same illumination specimens of Amjpkijdeura 

 pellucida, mounted dry, by Norman, were resolved and counted with 

 j^erfoct ease and remarkable plainness, the strias being still distinctly 

 visible with No. 3 eye-piece, draw-tube extended six inches, and 

 power upward of 10,000 times. It is with hesitation that he remarks 

 further that the 3^*^ ^'^^ resolved the lines of Ampliipleura pellucida 

 into rows of dots, for the " beaded " structure of the easier test, 

 Surirella gemma, is still doubted by some experienced microscopists. 

 But " facts are stubborn things," and the facts are that with Wenham's 

 parabola as an illuminator the dots are seen, and with either the para- 

 boloid or the Amici prism longitudinal lines much finer than the 

 transverse ones are brought out. These lines, which he considers 

 genuine, count not far from 120,000 to the inch. With a slight 

 change of the adjustment their place is occujaied by spurious lines 

 counting generally about 60,000 to the inch. The longitudinal lines 

 can only be seen when the focus is best adjusted for the transverse 

 strife. When the transverse lines are examined, they may be shown 

 smooth and shining, similar to the photograph by Dr. Woodward in 

 the ' American Naturalist,' but much better. If the mirror is then 

 carefully touched, a sinuate appearance of the margins of the lines 

 suggestive of beading is seen. This appearance can be brought out 

 readily. And finally, after the most painstaking manipulation, and 

 when without doubt the best work is being done, the separated dots 

 or beads appear. 



A Memoir on the Cyamus or Whale-louse has been published 

 in the ' Memoirs of tlie Scientific Society of Copenhagen,' by Dr. 

 Liitkeu. Wo believe it is an interesting paper, but we have not yet 

 seen it. 



