398 MR. G 8. WEST ON 
of one semicell are normal and those of the other reduced or 
absent, and by further division of such a plant a specimen may 
be produced in whieh the spines are entirely absent (fig. 4, e). 
On the division of this unarmed specimen, however the young 
semieells may develop typical spines, and it is interesting to 
g 
Arthrodesmus convergens, Ehrenb. All x 520. a, from Borrowdale, Cum- 
berland ; b, from Capel Curig, N. Wales; c-f, from Pilmoor, near Thirsk, 
N. Yorks. ` g, from Bowness, Westmoreland. 
note that a character which has been entirely lost is sometimes 
reproduced at its maximum development in a succeeding genera- 
tion (fig. 4, f, 9). 
It is highly probable that there is some direct relationship 
between tie unarmed forms of Arthrodesmus convergens, Ehrenb., 
and Cosmarium scenedesmus, Delp. (Mem. R. Accad. Sci. Torino, 
ser. II. tom. xxviii. 1876, p. 5, t. 7. ff. 28-34). 
