36 rrows OF THE MICROSCOPIC WORLD. 



THE PYXIDICULA. These minute organisms have received their scientific name 



from their form pyxidicula signifying, in the 1 Latin language, a 



Fig^ 37. Fig. 3& ^j g ^ QX They are enclosed in a transparent, spherical, flinty 



O^4t case, which is marked by a circular furrow through which it readily 

 |S1 divides, separating into two hemispheres. A group of a living 

 ^25^ species of the Pyxidicula is delineated in figures 37, 38, 39: a is 

 a view of the shell at right angles to that presented at &, and ex- 

 hibits the furrow through which it separates ; and c, is one of the 

 two hemispheres into which the shell divides. This organism is of 

 a yellowish-green color, and varies in length from one-fourleen 

 hundred and fortieth of an inch to one-five hundred and seventieth. It is quite 

 common, and is found both in a living and fossil condition. 



Fig. 40. THE ZIGZAG DIATOMS. Figure 40 is a drawing of a 



common Zigzag diatom, found by Dr. Mantell in the 

 neighborhood of London. These protophytes have re- 

 ceived the above appellation in consequence of their 

 being developed in zigzag chains, each link consisting of 

 a living organism. This mode of union arises from the circumstance that, although 

 the shells of all the diatoms are perfectly separated, their bodies are not, and thus 

 remaining attached, they present to view an irregular series, such as is displayed 

 in the figure. The flinty shell is three or four times as long as it is broad, is prisma- 

 tic in shape, and contains thirteen cross lines in every twelve-hundredth of an inch. 

 A narrow opening runs from one end of the shell to the other, through which cer- 

 tain processes are protruded, by the aid of which locomotion is effected. The 

 natural size of each shell of the chain in the engraving is one-four hundred and 

 thirty-second part of an inch. 



Fig. 41. In figure 41 is shown a cluster of another species of 



these diatoms, which, when imperfectly divided, are 

 attached side by side, and slide one upon the other the 

 entire group shortening and lengthening itself at, as it 

 were, at will. Their color is of an orange yellow, and 

 their length varies from one-two hundred and fortieth of 

 an inch to one-eleven hundredth. 



THE PALM, FAN-SHAPED DIATOM. A species of protophytes belonging to the type 

 of the Diatomaceae, and bearing the above name, is shown in figure 42. These 

 organisms are encased in a shell which is broad and wedge-shaped, and form a 

 fan-like cluster, rising from a single trunk or stalk. The stalk is produced by an 

 excretion of the plantule, and is not possessed of any vital power; for if the 

 branching, living groups are broken off, no fresh buds, teeming with vegetable life. 

 are put forth from the mutilated trunk, but it soon crumbles away and utterly 

 perishes. This organism increases by a longitudinal self-division, but the separa- 

 tion does not extend to the stalk ; for this remains entire while the diatom contin- 

 ues to develop in fan-shaped groups, the trunk branching into thick gelatinous 

 boughs, to which the separate vegetable atoms, gleaming with a golden hue, are 

 attached like fruit by a s'ender stem. This organism is found covering the surface 

 of marine plants. The natural size of the cluster varies from one-twelfth to one-sixth 

 of an inch that of a single specimen is one-one hundred and twentieth of an inch. 

 Figure 43 is a back and side view of a single individual, highly magnified. 



