STUDY OF THE GRAPTOLITES. 221 



undulating axis, to which tlie cell-divisions of one side are attached. In 

 the Retiolites of the Quebec group, one side of the stipe shows a very 

 distinct axis, while upon the other side it is very obscure* 



In Retiograptus, we have a very distinct central axis projecting below 

 the celluliferous portion of the stipe, and in one species, uniting in a 

 funicle, and forming part of a compond form. In another species, the 

 simple stipes present similar features, showing at one extremity the 

 duplicate character of the axis. 



In Phyllograptus, the central axis is apparently composed of four 

 slender flat laminae ; but we have had no means of examining this part of 

 the body in a satisfactory manner. 



2. THE COMMON CANAL,- COMMON BODY OR CCENOSARC. 



In all graptolites with a single series of cellules, there is, between the 

 bases of these cellules proper and the solid axis on the back of the stipe, 

 a continuous sub-cylindrical space or canal, which, in the living condition, 

 has been occupied by the common body of the polyp, from which the 

 buds, with their calycles forming the cellules, take their origin, and are 

 given off at regular intervals. 



All the specimens examined confirm this view ; and in some of the 

 species where the extremities are apparently entire, we observe the inci- 

 pient development of the young cell from the common body. In those 

 specimens filled or partially filled with the substance of the surrounding 

 rock, this canal is easily distinguished ; while in compressed specimens 

 there is always a flattened space between the bases of the cell-partitions 

 and the solid axis. 



In those graptolites with two ranges of cellules, we have apparently a 

 duplication of those with the single series, the two solid axes being joined 

 together, leaving a common canal or body on each side at the base of 

 each series of cellules. If, however, the common body were always thus 

 divided, it would be by the sold axis becoming a flattened plate. This 

 appears' to be true of some species (as for example, fig. 10, Plate ii); 

 while in others there is only a simple filiform axis visible, as in Clima- 

 COGRAPTDS. In this case, of course, there is not an entire division in the 

 common canal or body, after the manner of some other species. This 



* The assertion made by some late writers that Rbtiolites has no solid axis, is not sustained 

 by any specimens we have seen. The original description of Barrande, that it has no solid 

 axis as in Diprion = DiPLOGRApins, I suppose may be understood as meaning no dividing axis, 

 which probably exists in all that group proper ; while Climacograptus has a filiform axis, not 

 very unlike the axis of Retiolites. 



