lUO PROGRESS OF MICROSCOPICAL SCIENCE. 



can be separated from tlie mineral representing the sarcode, which 

 is described by Hoffinann as a cast of the soft parts of the Eozoon, 

 formed through iuliltration of watery solution either during the 

 growth or immediately after the death of the animal. It is a pecu- 

 liar silicate, fine-grained, greyish white, and somewhat translucent. 

 Associated with this is a finely granular dolomite, destitute of any 

 traces of organic structure, which sometimes appears to have served 

 as a centre or point of attachment to the growing Eozoon. In other 

 cases, however, broken fragments of older Eozoon had served as nuclei, 

 and become surrounded with a fresh growth. These materials, which 

 constitute what Hoffmann has described as the Eozoon reef, are asso- 

 ciated with two other silicated minerals. One of these, allied to fah- 

 lunite, has a specific gravity of 2'G87, is greyish brown or greenish 

 black in colour, dull, or with a somewhat fatty lustre, and nearly 

 opaque. This substance forms nearly parallel streaks in the central 

 parts of the Eozoon reef, and moreover surrounds it, intersecting and 

 wrapping around the Eozoon mass in multiplied layers, a line or more 

 in thickness, which are interlaminated with, a light green mineral, 

 transparent, with a somewhat vitreous lustre, and a density of 2-56. 

 It is a hydrous silicate allied to picrosmine, and is more or less pene- 

 trated by magnesite. 



Observations on Surirella gemma. — Col. Woodward has published 

 some recent observations on this species. The Surirella gemma has 

 been recommended by Hartnack as a test for immersion objectives of 

 high powers. Col. Woodward has not gained access to his original 

 description, but finds accounts of his views, with figures, in the works 

 of Drs. Carpenter and Frey.* Hartnack observed fine longitudinal 

 striae in addition to the fine transverse ones previously known to 

 exist between the large transverse ribs ; he supposed the true mark- 

 ings to have the form of elongated hexagons. Two handsome slides 

 of this diatom were received at the Army Medical Museum a few 

 months since, from Bourgogne, of Paris. A careful study of these 

 by monochromatic sunlight inclines Col. Woodward to the opinion 

 that Hartnack's interj)retation is erroneous, and that the fine striae 

 are in reality rows of minute hemispherical bosses ; from which, as 

 in the case of other diatoms, the appearance of hexagons would 

 readily result if the frustule was observed by an objective of inferior 

 defining power to that he used, or if the illumination was unsuitable. 

 This memorandum was accompanied by two photographs exhibiting 

 what he saw ; one was magnified 1034, the other 3100 diameters. 

 The principal frustule shown in these photographs was o^J o^th of an 

 inch in length. (The mean length of »S^. gemma is stated by the 

 'Microscopic Dictionary' at o^^yth of an inch.) The fine transverse 

 striae counted longitudinally at the rate of 72 to the r^V^*^ ^^ 

 an inch. Transversely these were resolved into beaded appearances 

 which counted laterally 84 to the yo'o^th of an inch. If the structure 

 consists, as he supposes it does, of fine hemispherical bosses, project- 

 ing from the surface of the frustules, the fact that these bosses are set 



* ' The Microscope and its Revelations,' 4th edition, p. 182. ' Dus Mikroskop,' 

 3rd edition, p. 40. 



