218 MR. W. ARCHER ON THE MINUTE STRUCTURE AND 
rachis. 'The next longest is that opposite thereto, external, and forming with the first 
an extremely acute angle (2); the third longest is that forming an obtuse angle with this 
latter ; and on it (3), as will be explained, stands the first joint of a branch; the fourth 
in length is that in apposition to the curved interior of the great notch in the lower part 
of the joint (4); and the shortest (which is very short) is that joining the last with the 
second longest (or that side bearing the branch) (5). When there are six sides the relative 
length of the sides is the same, and the additional side (6) is nearly equal in length 
to, and immediately under, that bearing the primary branch, and is itself (as will be ex- 
plained) surmounted by a minor shorter (stipule-like) branch. 
Now the mode of origin of these ramification-cells is seen to be by the formation 
of a peculiarly curved septum at one or (mostly) both sides of the joint of the rachis, 
previously cylindrical, or nearly so, all the way from its base to its summit—this septum 
beginning at its lower extremity from the point, about three fifths or two thirds from the 
base of the rachis-cell (before described), and ending at its upper extremity a little within 
the base of the joint immediately above (Pl. XXVIII. fig. 5). This septum (1) takes a 
sigmoid eurve as viewed from above, and is at the same time hollow or concave towards 
the ramification-cell, convex towards the rachis-cell, imparting the peculiar shape to the 
latter, as previously described. The cell thus eut off from the rachis-cell, as will be seen 
(it will of course be understood, when viewed from the “ front”), at first forms а scalene 
triangle—one side only, however (the outer), being quite straight, its lower end very 
attenuated, and its angle there very acute. 
In the formation of this septum we again encounter the curious character of an oppo- 
site pair of pits with their stoppers, every pit having its eorresponding opposite fellow, 
the likeness of а “rivet” being still carried out (omitted in the diagrammatic figure 5). 
The pair of pits in the new septum is placed about one third of the way upwards from 
the acutely angular bottom of the ramification-cell (а, fig. 10). Just as this cell is much 
smaller than the joint of the rachis, so the pits, with their stoppers, are much smaller 
than those at each end of thelatter. If ramification-cells are formed (as mostly, or indeed 
nearly always happens) at each side of the joint of the rachis (when formed at all), then 
the latter has two opposite lateral pits in its wall, in addition to the terminal; if only 
one ramification-cell be formed, then, of course, it has only one lateral pit. At this 
point, of course, the ramification-cell itself has but one pit—that is, the one opposite to 
and forming the fellow of the lateral pit of the rachis-joint. | 
The ramification-cell now soon grows out laterally in an inflated manner towards the 
upper end, the convex outgrowth being directed obliquely upwards (figs. 5 and 10). if 
viewed inverted, its noselike upper portion thus produced is now cut off by a curved con- 
cave septum, the concave surface being upwards—that is, the convex surface towards the 
cavity of the ramification-cell. The interposition of this septum makes the ramification- 
cell now five-sided—one of the sides (as before mentioned) being bounded by the septum 
just formed, the two adjoining sides, between which it intervenes, being the outer 
exposed portions of the ramification-cell now pushed out laterally, the upper one remain- 
ing very short and never further altered ; whilst the two remaining sides are, of course, 
those (as before mentioned) in apposition with the lower portion of the upper joint of the 
