November 22, 1895.] 



SCIENCE. 



693 



logical and not a sensory phenomenon, and 

 Prof. Le Conte's ingenious explanation becomes 

 unnecessary. 



In parentliesis, may I not ask whether since 

 the rods and cones are inverted, i. e., turned 

 away from the light, would not Prof. Le Conte's 

 ' push ' produce an inverted sensation ? 



That the rectification of the retinal image is 

 a matter of experience, will, I think, be readily 

 believed by any one who has worked much 

 with the microscope. The microscope also in- 

 verts the image, and when it is re-inverted in 

 the eye it falls on the retina rightly placed, that 

 is to say without inversion. A beginner finds 

 it almost impossible to move a preparation 

 under the microscope in the way he wishes, but 

 with practice the coordination of sight and 

 movement becomes so perfect that the adjust- 

 ment is unconscious. Now suppose a child had 

 inverted glasses kept permanently before its 

 eyes, so as to correct the retinal inversion, 

 would it not learn to adjust all its movements, 

 just as microscopists learn to adjust one set of 

 movements? In short would not that child 

 think it saw everything right side up ? Would 

 it be conscious of any peculiarity in its visual 

 conditions — of a great difference between it and 

 all other children ? I think, clearly not. 



Charles S. Minot. 



Haevaed Medical School, 

 November 11, 1895. 



SHELLS AS IMPLEMENTS. 



Editor of Science : Since writing about the 

 pierced mussel shells of Florida and from the 

 Shingu I have received a most obliging letter 

 from Dr. Karl von den Steinen, in which he 

 says : ' 'On the Shingu they scrape wood with the 

 pierced mussel Anodonta, while the Boror6 of the 

 Southern Lorenzo use the pierced SuUmus in their 

 woodwork. Oars, handles of axes and other 

 implements, bull roarers and bows are rasped 

 down and smoothed therewith. The objects are 

 not put through the hole for polishing, but the 

 mussel passes along them, the two edges of the 

 hole operate alternately and greater accuracy 

 of work and control over the implement are 

 secured. The edge of the hole is not necessarily 

 very sharp, neither does the workman retouch 

 the edges as would the flint worker. He simply 



throws the shell away, or makes another hole, as 

 do the Boror6 when it fails to work. 



' ' They make the hole with the point of a palm 

 nut, acuri ou the Shingu oukssu on the Southern 

 Lorenzo. Before making the hole they remove 

 the outer part of the shell with the teeth." 

 Dr. von den Steinen also sends drawings of the 

 Payaqua mounted spoon, with small, smooth 

 holes bored near the hinge to aid in the lashing. 

 I should like my colleagues to note this inter- 

 esting information in connection with the mus- 

 sel shells of the Southern United States, having 

 holes punched through them. 



O. T. Mason. 



A REPLY. 



Editor of Science — I note the criticisms in 

 Science for November 1st, which my friend, 

 Mr. Witmer Stone, has made upon my little 

 book, 'A Naturalist in Mexico,' and I beg 

 leave to answer the same through the columns 

 of the same paper. 



In the first place I wish to say that a foot note 

 was prepared for pages 13, 80, etc., but which 

 unfortunately did not appear in the pviblished 

 edition, and which was jsrinted as follows upon 

 a slip to be inserted in the volume. This slip 

 was not, unfortunately, placed in the first fifty 

 copies, and hence Mr. Stone's very just first 

 criticisms : 



Eeeata: For the account o£ the early discovery 

 and conquest of Yucatan, and for the measurements 

 of the ruins of Uxmal and Labna, the author is in- 

 debted to Stevens' ' Incidents of Travel in Yucatan. ' 



For the data used in the descriptions of the moun- 

 tains, and for the identifications, and some notes on 

 the birds, and of the land and fresh-water shells, the 

 author is indebted to the papers of Messrs. Heilprin, 

 Pilshry and Stone, published in the Proc. Phil. Acad. 

 Sci., 1890-5. 



Our next point is the description of the dif- 

 ferent measurements of Orizaba, which were 

 taken from Prof. Heilprin' s paper as a matter of 

 course, since the original papers from which he 

 took them were not at my command. The er- 

 ror of measurement by Dr. Kaska with a 

 ' thermometer ' instead of barometer is a typo- 

 graphical error. 



In regard to his next point I fail to see how 

 my short description of the birds could well be 



