CONTRIBUTION TO KNOWLEDGE OF EHABDOPLEUEA. 625 



to its predecessors by the so-called buccal shield or 

 prseoral lobe of the polypide. The structure of the tubes 

 is shown in Plate XXXIX, figs. 1 and 4. On exaroining the 

 tubarium of E-habdopleura in order to discover the law of its 

 growth, we find that it consists of a branching axis (PL 

 XXXVII bis, figs. 1 and 2, b), carrying throughout its 

 length numerous lateral appendages standing out from it, 

 sometimes on one side, sometimes on the other. These lateral 

 appendages have the form of long tubes with circular non- 

 dilated mouths. The axis presents no characters by which it 

 can be distinguished into primary, secondary, and tertiary 

 portions, the branches having always the same character as the 

 stock by the forking of which they arise. The axis is closely 

 adherent to the Ascidian test throughout its length, and is 

 often encrusted in its older parts by foreign growths. The 

 polyp-tubes form conspicuous objects from the fact that they are 

 attached like the axis itself for half their length to the ascidian- 

 test, and then, bending at a right angle, stand up perpendicular 

 to the surface of attachment. In the figure these perpendicular 

 tubes are represented without shading. No numerical law as 

 to the position of branches or the number of polypide tubes 

 given off" between one bifurcation of the axis and another can 

 be formulated. Branches usually arise by bifurcation, but 

 three or even four branches may sometimes originate in very 

 close proximity to one another. The arborescent form is 

 accordingly indefinite. The free extremities of the branches 

 present two different conditions. A branch often terminates 

 in an upstanding polyp-tube (see PI. XXXVII bis, d.). Such 

 a branch is a " completed branch," and is not in a condition to 

 produce any further polypides and polyp-tubes. On the other 

 hand, in many branches we can trace the axis to a considerable 

 distance beyond the last upstanding polyp-tube (PI. XXXVII 

 bis, a), pursuing a very straight course and closely attached 

 to the Ascidian test. This is a " growing branch. ^^ When 

 examined as to its contents, it is found that buds destined to 

 grow into numerous polypides are being formed within this 

 straight recumbent termination of the branch, and that it is 



