286 



THE MICROSCOPE AND ITS REVELATIONS. 



ance of a filamentous body covered in this way is often very elegant. >r 

 The frustules of Meridian are attached when young to a gelatinous 

 cushion; but this disappears with the advance of age. In the Family 

 Licmophorece also the frustules are wedge-shaped; in some genera they 

 have transverse markings, whilst in others these are deficient; but in 

 most instances there are to be observed two longitudinal suture-like lines 

 on each valve (which have received the special designation of vittce) con- 

 necting the puncta at their two extremities. The newly-formed part of 

 the stipes in the genus Licmophora, instead of itself becoming double 

 with each act of self-division of the frustule, increases in breadth, while 

 the frustules themselves remain coherent; so that a beautiful fan-like* 

 arrangement is produced (Fig. 172). A splitting-away of a few frustules. 

 seems occasionally to take place, from one side or the other, before the 

 elongation of the stipes; so that the entire plant presents us with a more- 



Licmophora flabellata. 



Fig. 173. Diatoma vulgare ; a, side view 

 of frustule; 6, frustule undergoing self-division. 



Fig. 17<l.Grammatophora serpentina:a, 

 front and side views of single frustule; 6, 6, 

 front and end views of divided frustule ; c, frus- 

 tule about to undergo self-division; d, frustule 

 completely divided. 



or less complete fldbella or fan upon the summit of the branches, with 

 imperfect flabellse or single frustules irregularly scattered throughout the 

 entire length of the footstalk. This beautiful plant is marine, and is 

 parasitic upon Seaweeds and Zoophytes. 



285. In the next Family, that of Fragillariece, the frustules are of the 

 same breadth at each end, so that, if they unite into a filament, they 

 form a straight band. In some genera they are smooth, in others trans- 

 versely striated, with a central nodule; when striae are present, they run 

 across the valves without interruption. To this family belongs the genus 

 Diatoma, which gives its name to the entire group; that name (which 

 means cutting through) being suggested by the curious habit of the 

 genus, in which the frustules after self-division separate from each other 

 along their lines of junction, but remain connected at their angles, so as 

 to form zigzag chains (Fig. 173). The valves of Diatoma, when turned 



