62 Transactions of the Royal Microscopical Society. 
“That, subsequently to this period, no change of configuration 
takes place in the siliceous valve, except along its margin, where 
fresh secretion of silex may, under certain circumstances, be pro- 
duced.” 
“That the normal figure of all markings whatever is circular, 
or approaches thereto.” 
“That these markings are arranged on the surface of the valve 
marginal rim which dips into a corresponding channel in the circumference of the 
connecting zones of this species. 
Fig. 10.—One of the connecting zones of B. turgida, showing the broad 
bevelled margin which is received within the body of the valve; the marginal rim 
of the latter fitting into the groove &, &. 
Fig. 11.—The connecting zone of B. turgida seen from its upper or valvular 
aspect. The sinuous outline of the bevelled portion is shown, and the two deep 
notches n, 7, and recesses r,7, which correspond to the positions of the bases of the 
spines and horns. (I have been quite unable hitherto to discover what purpose 
is served by the notches, inasmuch as the spines do not project into the interior 
of the valve. The presence of the notches would indicate, however, that there is a 
communication at these points between the interior and exterior of the structure ; 
this supposition being strengthened by the fact that the spines are very distinctly 
tubular.—G. C. W.) 
Fie. 12.—One of the T-shaped spines more largely magnified to show the two 
orifices of its tubule. 
Puate CLXXII. 
Fie. 1.—A frustule of /sthmia enervis from the middle of a filament, showing 
the great depth occasionally attained by the connecting zones of this species 
even before the new valves have been developed to any considerable extent. (This 
figure is copied from plate xlviii. of Professor Smith’s ‘Synopsis of the British 
Diatomacee.’) 
Fie. 2.—A frustule of Grammatophora serpentina, showing the two connecting 
zones; the right-hand valve having become separated by accident. 
Fic. 3.—A frustule of Chawtoceros (from the Indian Ocean), showing the con- 
necting zones c. z., c.z.; and a, a, the alternately crossing awn-like processes 
(abruptly cut off in the figure) by which the frustules are held together in fila- 
ment. 5 
Fic. 4.—A portion of a filamentous Desmid from Lower Bengal, viz. Onychonema 
uncinatum (Wal.), showing the same kind of alternate crossing of the horn-like pro- 
cesses as has just been referred to in Chetoceros. It may be said to be a common 
character in certain filamentous species both of the Diatomacee and Desmidiacee. 
Fic. 5.—A frond of Micrasterias pinnatifida: f, the constricted portion between 
the two segments. 
Fic. 5'.—a, a segment of the same which has separated from its fellow by the 
ordinary process of division; the new segment n.s. being developed by gem- 
mation from the constricted portion. 
Fic. 6.—The two valves of a frustule of Coscinodiscus Sol (Wal.). This beautiful 
diatom is figured for the purpose of showing the remarkable hyaline and mem- 
brane-like ring which surrounds each valve; the ray-like processes being given 
off from, and probably secreted through, the minute apertures which are present 
around the margin of the valve. 
Fie. 7.—T wo “ Sporangial Frustules,” a and 6, of an Hpithemia, formed by the 
fusion of the endochrome of either two or four normal frustules. The empty 
normal frustules and large sporangial frustules which contain the germs of the 
new generation being retained within the gelatinous mass, which becomes a 
nidus for the new brood as soon as it is set free from the sporangial frustules. ° 
Fic. 8.—The “ Sporangium” of a Cosmarium, formed, as in the case of the 
Epithemia, by the fusion of the endochrome of two fronds; so that, from first to 
last, it may be truly said that the processes of Multiplication and Reproduction in 
the Diatomacee and the Desinidiacee are almost identical, 
