1884.] 



MICROSCOPICAL JOURNAL. 



45 



The attractiveness and the delicacy 

 of this pretty creature ehide the pen- 

 cil and the graver. Be the portrait 

 ever so accurate, it still lacks the 

 charm of the living original. I have 

 never seen it, either standing alone or 

 as a true codosiga, without thinking 

 of a garden in the spring with its 

 lilies-of-the-valley blooming in the 

 shade. Associating it with the flow- 

 ers is a pleasure ; so, as a new species, 

 Codosiga Jlo7'ea^ let it be. The fol- 

 lowing description will probably be 

 sufficient for its identification : — 



Codosiga Jlorea^ n. sp. — Body 

 shortly campanulate, the length but 

 slightly exceeding the width, the 

 change in shape consisting chiefly of 

 an anterior marginal dilatation, usual- 

 ly rounded posteriorly, and bearing on 

 the anterior body-half a permanent 

 equatorially disposed groove ; pedicel 

 slender, eight to ten times the body 

 in height, the secondary pedicels 

 short ; contractile vesicles several. 

 Length of body ^^ to -^Jj^-inch. 

 Habitat. — Fresh-water. Solitary. 



Trenton, N. J. 



Structure of the Diatoin-ShelL — I. 



BY JACOB D. COX, LL. D., F. R. M. S., 

 PRES. AM. SOC. OF MICR. 



I propose to give some of the re- 

 sults of a series of observations upon 

 the structure of the diatom-shell, 

 reaching through a number of years 

 past, and of which my note-books 

 contain full memoranda. These ob- 

 servations have been repeated, varied, 

 and verified, until the conclusions 

 drawn from them seem to be based 

 on sound induction from solidly es- 

 tablished facts. I shall endeavor, 

 however, to state my methods of ex- 

 amination and the kinds of examples 

 used in such a way that students of 

 this department of microscopical bot- 

 any inay easily follow and repeat iny 

 experiments. 



In observations with transmitted 

 light I prefer balsam-mounted slides, 

 illuminated by a narrow, central pen- 

 cil of light. My illuminator has usu- 



ally been the Webster achromatic 

 condenser ^vith a metal slide behind 

 it having an opening a quarter of an 

 inch in diameter. When used with 

 lamplight a pale, violet-blue glass 

 modifier is behind the condenser. 

 Oblique light is necessary for the res- 

 olution of fine striae, and every method 

 of examination is to be used for com- 

 parison ; but the confusion caused by 

 shifting and crossing diftraction effects 

 at every change of the mirror is to be 

 avoided as likely to lead to error in 

 studying the shell-structure. Hence, 

 the choice of the small central beam 

 of light, made as free from glare and 

 cross-lights as possible. The object- 

 ive, on the other hand, should be. of 

 largest aperture, for experience and 

 comparison quickly prove that such 

 a glass has great superiority in the 

 way in which it takes hold of a sur- 

 face and defines the edges of areolae 

 and of fractured margins of the silici- 

 ous plates, and discriminates films 

 and lamineein different planes. 



Li working with reflected light, it 

 is worth while to seek every assist- 

 ance which skilful opticians can give 

 us. Every increase of power in the 

 examination of diatoms as opaque ob- 

 jects is a great gain, and there is no 

 direction in which painstaking labor 

 brings a better return. For this rea- 

 son glasses of large w^orking distance 

 are very desirable. Mr. Tolles' quar- 

 ter-inch objective with tapered nose 

 is a valuable lens for such purposes. 

 Bausch & Lomb are also making an 

 excellent quarter-inch of about sev- 

 enty-five degrees angle which can be 

 used on opaque mounts. Problems 

 which seem almost insohible when 

 objects are examined by transmitted 

 light are sometimes cleared up in a 

 inoment when they are treated as 

 opaque objects. 



The vertical illuminator also gives 

 us a mode of using reflected light 

 with high powers, the value of which 

 can hardly be overestimated. It is 

 sometimes said that it is only of use 

 for those parts of objects which are 

 in actual contact with the cover-glass ; 



