46 THE CANADIAN NATURALIST. [Feb. 



not been satisfactorily proved in regard to Dictyonema, and to 

 some other forms. 



In those species having a single series of cellules, this axis is 

 upon the back of the stipe, or on the side opposite to the cellulif- 

 erous margin ; and in the branching forms it follows all the 

 ramifications. In all the specimens where it has been observed, it 

 is a slender cylindrical or flattened filiform solid body. In some 

 extremely compressed specimens, this axis appears as a slender 

 elevated ridge along the back of the stipe ; and where the sub- 

 stance of the body has been removed, it leaves a narrow groove 

 along the margin of the impression. 



In the examination of large numbers of specimens of the mono- 

 prionidian species, we have never found the axis prolonged beyond 

 or denuded of, the cellules; as shown in G. colonus, by Barrande, 

 in his Graptolites of Bohemia. 



In all the specimens where the extremities of the stipes are 

 entire, (as represented in plates i, ii, and iii of the memoir,) there 

 is never any extension of the axis beyond the last partially de- 

 veloped cellule ; and the number of specimens in this condition is 

 considerable. 



In the graptolites with two series of cellules, the solid axis is 

 very frequently seen extending beyond the celluliferous portion of 

 the stipe at its outer extremity ; while the radicle appears like the 

 continuation of the same below the base. The axis thus appears 

 to be the foundation on which the other parts are erected. In 

 those specimens, however, which present so great an extension of 

 the solid axis beyond the stipe, the cellules may have been removed 

 by subsequent causes. 



I am able to corroborate to some extent the observations of M. 

 Barrande in regard to the apparent double character of this axis. 

 In some extremely compressed specimens it is marked by a longi- 

 tudinal groove or line of division;* while in others, a double 

 impression has been left by the removal of the substance. 



2. The Common Canal. — 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 has been occupied by the body of the polyp, 



* The aspect presented by the axis, when marked by a longitudinal 

 groove, is precisely that which a hollow cylindrical body would have if 

 extremely compressed. 



