34 



YIEWS OF THE MICROSCOPIC WORLD. 



Fig. 



ochre. This species of G-allionella is found both in a recent and fossil state, and 

 measures only one-twelve thousandth of an inch in diameter. 



THE NAVICULA. The Navicula. both recent and fossil, forms a very interesting 

 class of the diatoms; it is shaped like a boat or ship, and from this resemblance has 

 received the name of Navicula, which in the Latin language signifies a little ship. 

 Thev are never united, like the Gallionella, in chains; but exist singly and in pairs, 

 enclosed in a durable, thin, siliceous cell, generally four-sided, and which, when 

 slio-htly pressed, divides either into two or four parts, disclosing the appearance of 

 ribs running across it. A jelly-like substance, which constitutes the body of the 

 plantule, occupies the interior of the shell, and portions of matter, of a green, yel- 

 low, and brown color are here perceived, which were once regarded by naturalists 

 as the eggs of the* Navicula. Many of the Ship-Navicula propagate by self-division 

 in the two directions of their length and breadth ; the separation commencing 

 in the soft body beneath the shell, which afterwards divides into parts cor- 

 respondino- to those of the body. Twenty-four different kinds of fossil Navicula 

 have been discovered, fourteen of which have been identified with species now 

 living. 



G-REEN NAVICULA. Figure 30 is a drawing of this diatom, representing a speci- 

 men taken by Dr. Mantell from a pool in Clapham Common, in the vicinity ol 



London. The small dots which Ehrenberg 

 supposed to be stomach-cells, and the rib-like 

 divisions of the shell, are distinctly seen 

 throughout its whole extent. So numerous 

 are they, that fifteen are contained within 

 every twelve-hundredth of an inch in length. 

 A side view of the same individual is 

 shown in figure 31, exhibiting the currents 

 produced by its motion through the water. 

 This species of Navicula varies in size from 

 one-seventieth to one-one hundred-and-fifteenth 

 part of an inch in length. 



GOLDEN NAVICULA. Figures 32 and 33 are representations of a beautiful 

 species of the golden Navicula, so called because the clusters of globules 



within the shell are of a bright-yellow color. 

 They are seen in the engraving occupying the 

 central portions of the shell, and filling up its 

 numerous flutings. The shell is of an oblong 

 oval shape, and possesses the utmost regularity 

 in its structure. In figure 31, the Navicula is 

 seen from above; in figure 33, a side view of 

 the same diatom is presented: by comparing the 

 two drawings, it is seen that the shell tapers 

 more in the latter case than in the former. The 

 above figures are faithful delineations of a living 

 golden Navicula obtained by Dr. Mantell: the 



