39 



which the cellules were placed. It is probable that this slender 

 cylinder contained a minute portion of the body of the organism, 

 as it appears to have possessed the power of growing independently 

 of the general body, and in some cases to have extended a 

 considerable distance beyond each end of it. This vital part of 

 the axis, if such existed, does not appear to have had any 

 connection with the general body, in the common canal, and 

 could not derive nourishment therefrom. The chief function of 

 the axis was no doubt to give stability to the polypary. 



The "common canal" (Fig. 4), in which the "ccenosarc" or 

 general body was enclosed, consisted of a tube formed of horny 

 material. On one side of this tube, in single Graptolites, was 

 placed the axis, generally outside the tube ; and on the opposite 

 side were the cellules containing the Zooids. 



The "cellules" (Fig. 5) were small cups formed of the same 

 horny substance as the other parts of the polypary, and were 

 placed side by side, along the common canal. Except in one or 

 two forms, the cellules do not spring vertically from the common 

 canal, but are inclined, at various angles, towards the upper, or 

 distal end ; and thus each cellule overlaps its neighbour to a 

 - certain extent. 



Until quite recently, the opinion held generally by palaeontolo- 

 gists respecting the structure of all forms of Graptolites, was that 

 the cellules opened full into the common canal, and that the 

 ccenosarc was a continuous body throughout the entire length of the 

 common canal. A structure differing from this was first observed 

 by Professor McCoy, who in describing a Graptolite from the 

 Skiddaw Slates, to which he gave the name of Graptolites latiis, 

 speaks of "transverse diaphragms" being present near the base of 

 the cellules. This appeared in his British Palceozoic Fossils, 1854. 

 No additional light was brought to bear on this peculiar structure, 

 until Mr. William Kinsey Dover of Keswick directed the attention 

 of Mr. Hopkinson to some specimens in his collection, which 

 show not only that each cellule was cut off from the common 

 canal by a clearly-marked septum, but that the common canal was 

 also divided by transverse septa between each cellule (Fig. 6). 



