330 



Kig 1 . 335. Cottoniella arcuaia nov. spec. 



a, upper part of a filament with branchlets and a young branch, b, summit 

 of a filament showing the endogenous origin of the branchlets. c, branch 

 issued at the side of a branchlet. d, base of a branch, e, /', g, transverse 



sections of the thallus. 

 (a, about 220:1. b, 450:1. c and d, 320:1. eg, 250:1). 



on the left side of the branchlet, but probably this is only by chance, 

 for I have also found them placed on the right side ; sometimes, too, 

 a branch happens to be issued from a segment without any branchlet. 

 In the first stage of development the branches are very like the 

 branchlets, but longitudinal walls are soon developed, dividing the 

 segment into a central and four pericentral cells. 



The segments are, immediately after they are cut off from the 

 apical cell, very short, but gradually they increase in length becoming 



