ZOOPHYTES. 327 



fine thread of a pellucid white appearance, so firmly 

 adherent that if you attempt to remove it with a needle's 

 point, you find that you only tear either the leaf or the 

 thread. The course is generally 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, however, 

 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 direction 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 examine 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 their 

 branches are similar tubes, whose cavities are in free com- 

 munication with that of the creeping root. The wall is 

 thin, and perfectly transparent and colourless ; the white- 

 ness of the whole being dependent on a soft medullary 

 core of living jelly, which permeates the whole structure, 

 on which the horny sheath is, as it were, moulded. 



This medulla is pierced with a canal, through which a 

 fluid circulates, carrying along numerous minute granules 



