ZOOLOGY AND BOTANY, MIOROSCOPY, ETC. 787 



as " vegetable sozodont toofh powder," he finds it to be composed 

 chiefly of diatomaceous material, the forms being in both perfect 

 and fragmentary states. Various forms of Navicula and Pinnularia 

 occur in great abundance, and when mounted in balsam the powder 

 makes an interesting object. 



Strise of the Diatomacese.* — The Count (Abbe) Castracane has 

 published a paper under the title " On the value to be attributed in 

 the Determination of Species to the number of the Striee of the Diato- 

 maceffi," of which the following is substantially a full translation — the 

 original paper is written in Italian. 



" One of the most fortunate epochs for sciences of observation is, 

 without doubt, this half of the nineteenth century, when the attention 

 of theoretical and practical opticians being applied to the construction 

 and perfecting of the Microscope, a new path has been opened for this 

 instrument with a more brilliant future, thanks to Professor Amici 

 and his invention of immersion objectives. Objectives of the highest 

 magnifying powers will now give greatly improved images as regards 

 spherical and chromatic aberration, and beyond all other advantages 

 realized in this way, a much more valuable victory and a much greater 

 progress was the extent of the angle under which the object could be 

 illuminated. It is thus that organisms presenting details of exquisite 

 fineness, and which seemed to defy all power of resolution, have been 

 shown and distinguished from one another by the use of very oblique 

 illumination, so that this angle of apertui-e of objectives is the principal 

 factor of their value. 



The acquisition of an instrument of research so interesting and so 

 ef&cacious, has led to the discovery of unexpected wonders, and the 

 Microscope has become the inseparable companion of the naturalist, 

 the physician, the botanist, the physiologist, and all those who 

 endeavour to recognize the ultimate forms and the minute structure of 

 organisms and tissues. The Microscope has opened new fields to the 

 insatiable curiosity of mankind thus drawn towards the study of the 

 wonders of the microcosm. Amongst the latter must certainly be 

 reckoned the Diatomace^, the knowledge of which, we may say, only 

 dates from the time when the improvements of which we have just 

 spoken were introduced into the construction of the Microscope. 

 This revelation has furnished the most abundant harvest of discoveries 

 to those who have devoted themselves to such researches, and it is not 

 surprising that Ehrenberg, Kiitzing, Smith, Brebisson, Gregory, Bailey, 

 and many others, have been able to recognize so large a number of 

 diatoms, whilst all those who have occupied themselves seriously with 

 this study know that the discovery of new genera and new species is 

 not very difiicult, although the selection of these new species is far 

 from being perfect. 



But the work of those to whom we are indebted for the knowledge 

 of thousands of forms of the Diatomacese must necessarily suffer the 

 consequence of the rapidity with which the number of the new 



* Atti Accad. Pontif. Nuovi Lincei, xxxi., Sess. VI., 26th Mav, 1878. See 

 Journ. de Microgr., iii. (1879) p. 283. See also this Journal, i. (1878) p. 152. 



