24 CANADIAN FOSSILS. 
G. divergens, where the continuation of this common rachis is marked by 
marginal cellules of the same character as those of the lateral stipes. 
The common body therefore appears to perform the double function of 
developing the buds which elongate into stipes with cellules, and also of 
simple cellules; or we may consider the celluliferous extremity of the 
rachis, or main axis, as the termination of the reproductive process, or 
as analogous to one of the lateral celluliferous stipes. In the Sertula- 
rians we have something analogous to this mode of development. Some 
of the species have cellules along the common or main trunk, and produce 
at intervals branches or branchlets in place of cellules; others have a 
common body, or main stem, entirely destitute of cellules, but producing 
branches on each side (opposite or alternate, as the case may be), which 
branches produce cellules only. 
So long as this rachis gives off only celluliferous stipes, it is analogous 
to those parts of the simple graptolites which I have termed the funicle, 
having within itself the sources of this development of the several parts. 
The mode of development differs from that of the branching forms, inas- 
much as the branches proper arise from a division of a cell-bearing stipe 
or branch, and of course a division of the solid axis and common body. 
In Retiograptus, some specimens show the cell-divisions reaching nearly 
to the axis, leaving room on each side for a narrow common body or canal ; 
while in a species from the Utica slate, which presents one side of an 
entire frond, the cell-divisions of the exterior side all reach to the axis, 
leaving the common body on the inner or upper side. In a species from 
Norman’s Kill, near Albany, there are three parallel ranges of reticu- 
lations, with apparently two filiform solid axes, forming the divisions 
between the three meshes. This structure probably occupies one side of 
the stipe, while the common body may occupy the other side. 
In Phyllograptus, the cell-partitions reach very far towards the centre, 
and the space left for the common canal is very small. We infer from 
the better-preserved specimens that there is a slender common canal at the 
base of each range of cellules. These several canals may or may not 
communicate with each other. 
3. The Calycles or Cellules: their form and mode of development.— 
Since a large proportion of the specimens of graptolites which come under 
our observation for the purposes of study or otherwise, are fragmentary, 
it becomes of much importance to know the general characters of form and 
mode of development of the cellules. 
In the preceding section it has been shown that the cellules, or the 
inhabitants of these cellules, are not independent, but all have their origin 
in a common body, which fills the longitudinal canal, and that they remain 
in constant connection with the same throughout their existence. 
The calycle or cellule is formed by budding from one side of the com- 
