I02 



THE AMERICAN MONTHLY 



[June, 



by sunlight with a 2V inch objective by 

 William Wales, and the magnification 

 was, in two instances, 2470 and 2740 

 diameters respectively. 



In the accompanying engraving (fig. 

 18) we have very accurately repro- 

 duced portions of the two photographs. 



The drawing was made on the 

 block by Mr. E. Q. Morton, and is a 

 very faithful copy of the photographs. 

 On the left-hand half is represented 

 the appearance of the test-podura- 

 scale. Some of the spines show the 

 appearance of a distinct head to the 

 internal line of light, such as was 

 described in Vol. III., page 225. We 

 regard this as a very correct repre- 

 sentation of the appearance of the 

 test-podura scale, as shown by good 

 objectives. We believe that Mr. 

 Wales considers it to be the proper 

 appearance of the spines. 



On the right-hand half of the figure 

 are shown some detached spines, not 

 of the podura, but of the insect De- 

 geria dotnestica so closely allied to it, 

 that it may be fairly assumed the 

 structure of its scales is the same. 

 The remainder of the engraving shows 

 a portion of the scale from which the 

 detached spines came, quite out of 

 focus, however, as the photograph 

 was made to show the detached spines. 

 The later were separated by accident. 

 The accident was a fortunate one, as 

 it enables us to see the separate spines, 

 thus proving that they have an exist- 

 ence, and disproving some views that 

 have been advanced in the past con- 

 cerning the structure of the scale. 



Some readers will doubtless remem- 

 ber that the spines of podura have 

 been separated from the scales by an 

 electric spark, so that they could be 

 seen and studied in a similar manner. 



Binocular Yision. 



[At a meeting of the Royal Micro- 

 scopical Society of London, held some 

 time ago, Mr. F. Kitton read an ar- 

 ticle on " Binocular Vision in the 

 Study of Diatomaceae." As the ad- 

 vantages of binocular vision are still 



doubted by many observers, the opin- 

 ions of several gentlemen whose names 

 are well known to all microscopists, 

 may be read with interest. — Ed.] 



Mr. Beck said, that with reference 

 to the opening remarks of the author 

 on the value of binocular over monoc- 

 ular vision, he could fully bear out all 

 that had been said. A valuable means 

 of convincing any one who was scep- 

 tical on the subject was to be found in 

 a slide of Aulacodiscus ; and he re- 

 membered that when his brother 

 Richard showed this diatom to Mr. 

 Tuffen West for the first time under 

 the binocular, that distinguished 

 draughtsman looked at it for some 

 time in silence, and then jumping up, 

 exclaimed: 'All the drawings of dia- 

 tomaccK which I have done will have 

 to be done over again ! ' 



Dr. Wallich said that he could fully 

 confirm the statement that nothing 

 showed diaioms so well as the binoc- 

 ular. Indeed, from a study of these 

 objects, extending over many years, 

 he could say that it was utterly impos- 

 sible to see them in any other way. 

 In one of the drawings of Hydrosira 

 he observed that Mr. Kitton had not 

 noted the unsymmetrical formation, 

 consisting of a little dot, which was 

 generally surrounded by a slight ridge 

 on one side only. It occurred in Hy- 

 drosira and many of the discoidal 

 forms, and though often seen, he had 

 never yet been able to detect what 

 this peculiar structure was. It would 

 be of advantage if some one would set 

 to work to determine it. It seemed 

 to him to have something to do with 

 the communication between adjacent 

 frustules. 



Mr. Crisp said that Mr. Kitton had 

 proved conclusively the superiorityo f 

 the binocular, in that he had shown 

 the true form of diatoms, which had 

 previously been misinterpreted by 

 most experienced observers after ob- 

 servation with the monocular. 



Mr. Stewart said that there were 

 still some persons who appeared to 

 think that the binocular was a mere 

 toy. It was, however, of really great 



