376 EVENINGS AT THE MICEOSCOPE. 



"With the unassisted cje Ave can discern plainly 

 enough the outline and plan of this compound organ- 

 ism. Along the smooth and lubricous surface of the 

 olive weed runs a fine thread of a pellucid white ap- 

 pearance, so firmly adherent that if you attempt to 

 remove it with a needle's point, you hnd that you only 

 tear either the leaf or the thread. The course is gen- 

 erally in a straight line, but does not ordinarily pursue 

 the same direction far, commonly turning off with an 

 abrupt angle at intervals of about an inch, and thus 

 meandering in a zig-zag fashion, very irregularly, 

 branching frequently, and uniting with a thread already 

 formed, when the creeping one has to cross it. 



Thus the basal network is formed ; but meanwhile, 

 from every angle, and often from intermediate points, 

 a free erect thread has shot up — like the stem of a tiny 

 plant — to the height of an inch, rarely more ; not, how- 

 ever, straight, but with frequent zig-zag angles, whence 

 the name geniculata, or " kneed." At every angle a 

 slender branch is sent forth, pursuing the same direc- 

 tion as that of the joint from the summit of which it 

 issued, and terminating in a tiny knob. In the angles 

 of some of these branchlets are seated oblong vesicles, 

 twice or thrice as large as the terminal knobs. And 

 this is pretty well all that we can make out with the 

 naked eye. 



Cutting carefully off with scissors a narrow strip of 

 the leaf, I drop it into the parallel-sided cell of glass 

 half-filled with sea-water, and examining it first with a 

 low power, and afterwards with a higher. We now see 

 that the creeping thread is a tube of horny substance, 

 flattened on its under side, and that the erect stems and 

 tlieir branches are similar tubes, ■whose cavities are in 



