'210 
F r i t s c li. Studies 011 Cy anopliy ceae. 
sliort rows of cells of Synechococcus otherurse recall Oscillaria to 
a great extent. 
Dangeard (99) in his exceedingly instructive paper on the 
evolntion of sexuality has shown conclusively, that the filament 
or row of cells is the niost advantageous front the nutritive 
point of view: and quite in correspondence with this ve find 
that in the Cy anopliy ceae, as in other algal phyla, the filament 
is the most successful form. The celi-sheath, which in Gloeo- 
capsa and other unicellular forms, constitutes a firm investment 
around the whole cell, is only necessary laterally, when the fila- 
mentous stage is attained. By the rapid succession of divisions 
all in one direction no time is given for the closure of the gap. 
left in the celi-sheath, whilst by a suppression of the mucilage, 
excreted between the products of division, a consistent trans- 
Rividaria 
Tolypothrix 
Anabaena (Nostoc) 
Lyngbya 
A 
Oscillaria 
T A 
\ p 
<5 
CD 
O 
0 
O 
Gloeothece 
A 
Synechococcus 
A 
i 
CD 
ci 
m 
i 
G loeocapsa Merismoped ici 
Äphanothecc 
verse septum originates, which completely replaces the celi- 
sheath at this point. In this way the state of affairs, occurring 
in Anabaena. is attained. It should be noted that eacli cell of 
> ... • 
the filament still retains its individuahty to some extent, m so 
far as it has its own peculiar cell-slieath, probably excreted 
primarily by eacli individual cell, and, in so far as in the 
course of division of a cell, already provided with such a celi- 
sheath, the latter is split into two portions, appertaining to the 
daughter-cells. It seems probable that this Splitting is merelv 
due to the relatively strong development of the intercellular 
septum, which is certainly more strongly developed liere than 
in a form like Oscillaria , — a point of resemblance to Gloeo- 
capsa etc. 
