STUDY OF THE GRAPTOLITES.- 191 



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 colluliferous portion of the stipe, and, in one specfes, uniting in a 

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

 simple stipes present similar features, showing at one extremity the dupli- 

 cate character of the axis. 



In Phylloqraptus, the central axis is apparently composed of four 

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

 the body in a satisfactory manner. 



2. The Common Canal, the Common Body or Ccenosarc. — In all grapto- 

 lites 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 thrown 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 incipient 

 development of the young cell from the common body. In those speci- 

 mens filled or partially filled with the substance of the surrounding rock, 

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

 always a fiattened 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 solid 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 Climacograptus. 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 feature is shown 

 under the illustrations of the structure of these bodies on Plate ii. 



In Retiolites, the common body occupies the central portion of the 

 stipe, giving origin to a series of buds or polypites on each side, while the 

 central axis is filiform and does not divide the interior canal. 



In some species, the common body seems also to have more extensive 

 functions ; for in such forms as G. diver gens and G. gracilis, there is a 

 long slender rachis, or tubular body, destitute of cellules except at its two 



•,Thc assertion made by some late writers that Retiolites 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=Diplo6RAPtus, I suppose may be understood as mean- 

 ing no dividing axis, which probably exists in all that group proper; while Cum acoguap- 

 Tus has a central filiform axis, not very unlike the axis of Retiolitks. 



