Objects for the Microscope. 45 



NAVICULA HIPPOCAMPA. 



The Navicula? comprise the largest section of the whole 

 body of diatoms, and vary very much in form and markings, 

 but the genus Navicula? itself is so called from its resem- 

 blance to a boat or little ship (Nave, a ship). They are 

 found, both in the living and fossil state, of a bright golden 

 colour, the valves delicately striated, with or without a 

 central aperture. Some are striped longitudinally ; some 

 transversely ; some waved or shaped like the letter S, as 



PLEUROSIGMA 



in which the apparent stria? are resolvable into hexagonal 

 dots under a high power. These Navicula? all multiply by 

 division and conjugation, as do the diatoms generally, 

 which cannot be explained without plates, and the student 

 must refer to the works already mentioned. 



MELOSEIRA, 

 From melos (a member), and seira (a chain), 



is found on marine algse, a composite plant of man^ 

 frustules, joined together by siliceous hoops. 



MELOSEIRA BORRERI. 



No student should be without a slide of Meloseira, 

 because it is a diatom very likely to be mistaken under a 

 low power for a mass of conferva?. In fact, it has been 

 misunderstood even by eminent naturalists. Agardh, the 

 Swedish botanist, found and classed it with the fresh-water 

 alga? ; Ehrenberg examined and removed it into the animal 

 kingdom under the name of Gallionella; and now it is 

 replaced in the vegetable world as a diatom, its siliceous 

 lorica being quite ascertained, and many beautiful species 

 found both in salt and fresh water. If possible, obtain a 

 specimen of Meloseira sub-flexilis, which is found off 

 ifriburg ; or Meloseira nummulites, found in the Baltic Sea ; 

 but meanwhile observe this M. Borreri, which is abundant 

 on marine alga?. You see a mass of bead-like filaments, 

 which towards the edge is better seen and with a high 



