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tracted endochrome by a transparent interval, and frequently 
presenting in its interior, at each extremity, a minute nucleus- 
like body, with strong refractive powers. 3. An external very 
delicate, but well-defined transparent investment, which is pro- 
bably continuous with the general gelatinous (?) investment of 
the filament. 
At first, no other kind of cell beyond those now described 
could be detected in the filaments, but in specimens gathered 
somewhat later many filaments presented in some part of their 
course a long cylindrical and slightly dilated cell, generally 
about two or three times the length of the heterocysts; occa- 
sionally a single filament presented two such cells. They 
correspond to the cells named sporangia in the other Nosto- 
chine; their contents are always minutely granular, and under 
the action of iodine contract towards the centre, and then pre- 
sent a very definite boundary, in which a double outline can 
sometimes be distinctly seen ; while, external to this, and sepa- 
rated from it by a clear space, a colourless investing membrane 
has become very obvious; but the second investment, so evident 
inthe heterocysts, could not here be satisfactorily demonstrated : 
the little spherical body visible at each extremity of the cell of 
the heterocyst could not be seen in the sporangium. Fila- 
ments bearing sporangia were accompanied by those bearing 
heterocysts, but whether the two kinds of cells ever coexisted 
in the same filament was not manifest. 
That the sporangia are not simply enlarged cells, but the 
result of the union of several ordinary cells, is evident. ‘The 
author has succeeded in observing them in intermediate stages 
of formation, in which the endochrome of a group of ordinary 
cells had already begun to assume the minutely granular con- 
dition of that of the sporangium, the septa being, at the same 
time, evidently in process of disappearing. 
Aphanizomenon Flos-aque, after the death of the plant, is 
eminently sensitive to the action of light. Specimens dried on 
