148 THE AMERICAN MONTHLY [May 



simple mechanical coarse adjustment which appeared to be 

 a modification of the Plossl just described. The connect- 

 ing^ links of the latter form were omitted ; radial slots cut 

 throug-h the milled heads eng-ag-ed the stud pins fitted on 

 the sides of the body, so that when the milled heads were 

 turned throug-h a part of a circle, the body was raised or 

 lowered. In a yet smaller microscope there was an inge- 

 nious detail of construction in the method of securing the 

 outer tube to the limb, by inserting the screws from the in- 

 side of the tube, and screwing into the limb, a much supe- 

 rior plan to that of putting- them in from the other side. 

 There was, likewise, a diminutive microscope measuring- 

 about 3 in. high, of a cheap type. The next microscope was 

 sent by Mr. Ernest Barker. It was a pocket form, the case 

 measuring-, when closed, 4^in. by 2in. by l^in. It was an 

 ingeniously arranged little instrument, and very suitable 

 for field work. Mr. Nelson read an extract, kindly sent by 

 Mr. Jerome Harrison, of Birmingham, from Dr. Hooke's 

 "Microscopium" (1678), describing- .i method of using con- 

 vex lenses ("g-lobules") by contact with water. Mr. Nel- 

 son thought it extremely interesting- to know that the im- 

 mersion objective was not such a modern invention as was 

 generally supposed. He said Mr. Powell had just pointed 

 out to him that these lenses of Hooke's differed from the 

 immersion objectives of the present day, which had flat 

 fronts, whereas in Hooke's lenses the water was applied to 

 convex surface, which soformed a sort of concave lens, and 

 corrected, to some extent, the chromatism of the glass. 

 Messrs. Swift exhibited a new pattern microscope, the up- 

 per portion of which was a replica of the Continental form 

 while the lower part was of the English type. 



Mr. Rousselet read a note in reference to a large selec- 

 tion of slides of new, rare, and foreign rotifera which were 

 exhibited under about thirty microscopes. Special refer- 

 ence was made to specimens of Trochosphaera solstitialis, 

 Aprilus lentiformis, and Asplanchna herricki, which is 

 much like other species of Asplanchna in shape, but po«^- 

 sesess a small glandular organ withtubeopeningoutwards, 

 which is not known to occur in any other rotifer, and the 



