192 TWENTIETH REPORT ON THE STATE CABINET. 



extremities, and apparently consisting of a solid axis and a common body, 

 from which originate, at regular intervals, simple small stipes with solid 

 axis, common canal, and cellules. 



This appears to be one step farther in our knowledge of the origin or 

 mode of development ; but it shows that a common body or main axis may 

 produce in one part celluliferous stipes, and its extremities develope only 

 cellules, as we see in the continuation of the main axis of G. gracilis and 

 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 {Ccenosarc) appears to perform in this case the 

 double function of developing the buds — polypites, which elongate into 

 stipes with cellules, and also of simple cellules at its two extremities; or 

 we may consider the celluliferous extremities of the rachis, or main axis, 

 as analogous to one of the lateral celluliferous stipes. These individual 

 stipes, if separated from the main axis, would have the appearance of 

 entire graptolites with the attenuate lower extremities ; and it seems to 

 me not improbable that some of the simple monoprionidian species, which 

 have been regarded as entire bodies, may in fact be only the separated 

 portions of fronds like that of G. gracilis and similar forms. In the Ser- 

 tularians 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 

 bear 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 th« 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 Ketiograptus, 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 other side.* In a species from Nor- 

 man's Kill, near Albany, there are three parallel ranges of reticulations, 

 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 expression here used is from an idea that the original form of the frond is funnel- 

 shaped; and the inner side, upon which the common canal would be visible, now lies 

 against the stone. 



