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POPULAR SCIENCE REVIEW. 
segments in the Desmid and the new valves in the Diatom are 
represented as taking place). 
E 
A. a , front view of a valve of Navimla, showing the endochrome arranged in two 
longitudinal lamellae along the margins of the valve ; b, front view of the 
frustule ; wheir dividing, the endochrome here seen will divide longitudinally 
along its centre. 
B. Front view of frustule of Nitzschia, showing the endochrome in this view as if 
it consisted of only two portions ; the nucleus centrally situated, and the ter- 
minal vesicles at the extremities, precisely as in Closterium (fig. 2). The 
peculiarity of this genus consists in the endochrome being divided into four 
lamellae, not parallel with the plane of the valves, but of the connecting zones. 
C. A short filament of Himantidium, showing the curious fourfold curtain-like 
arrangement of the true endochrome, the nucleus as usual central. 
D. d, front view of a frond of Docidium, a Desmid, intended to showthat by cutting 
off the ends of the segments, s s, at the points indicated by the dotted lines, the 
front view would closely resemble the front view of the frustule of Melosira (a 
Diatom ), of which the outline is given as E, the sectional outline or end view of 
the Docidium being represented as e v. 
In the Diatom, as soon as division is completed, the true 
endochrome of each frustule splits up into two, and in some 
genera four, lamellar masses, each of which, from its remaining 
