Nicholson — On Graptolites. 261 



species are, as far as my experience goes, totally absent. In the 

 case, then, of the Hart Fell species, such as Diplograpsus pristis, D. 

 teretiusculus, D. miicronatus, Didymograpsus flaccidtis, D, sextans, etc., 

 it might be assumed with some probability, that the gonophores 

 were unprovided with a corneous envelope, and were therefore in- 

 capable of leaving any traces of their existence. I do not, of course, 

 assert that this absolutely was the case; I merely start it as an 

 hypothesis, capable of explaining the apparent absence of the capsules 

 in certain localities. Whilst cases such as the above occur, it should 

 be borne in mind that the capsules have never yet been found except 

 in rocks where Graptolites abound; whilst they present the most 

 striking similarity in form to the gonophores of many recent Hydro- 

 zoa. Further, if the capsules do not stand in some relation to the 

 Graptolites, but are to be considered as independent organisms, it 

 appears to me that the palgeontologist will be compelled to create a 

 new family for their reception ; since, I venture to say there is no 

 known genus, or family, to which they could with any likelihood be 

 referred. I may add, finally, that even in the total absence of re- 

 productive bodies, or of any proofs of their direct connexion with 

 the Graptolites, I should still think the evidence very strong against 

 the view, that the Graptolitida are referable to the Polyzoa. I rest 

 this statement upon the fact, that the true Graptolites (omitting 

 Dictyonema, and with the possible exception of Dendrograpsus and 

 Callograpsus) are all free, whilst the Bryozoa are invariably fixed ; 

 upon the undoubted presence of a " common canal " in many,^ if not 

 in all, of the former ; upon the mode of growth and nature of the 

 embryonic forms ; upon the absence of calcareous matter in the test ; 

 and upon the existence of allied forms, like Corynoides. Should the 

 views, which I have briefly expressed concerning the nature of the 

 " capsules," be confirmed by future and more extended observations, 

 the zoolog-ical position of the Graptolitidce will no longer be a matter 

 of doubt, and they can unhesitatingly be classed amongst the Hydro- 

 zoa. This is a subject which I trust to take up hereafter in greater 

 detail, and I must at present content myself with stating that I do 



^ I altogether question the absence of the " common canal " in any true Graptolite ; 

 though Mr. W. Garruthers has recently denied that it exists as a distinct structure, 

 referring especially to Diplograpsus pristis, His., D. folium, His., I), cometa, Gein., 

 and Graptolites Sagittarius, Linn. (Geol. Mag. Vol. IV. p. 70). In this opinion Mr. 

 Garruthers stands, I helie-ve, alone amongst those who have written on the subject; 

 and Hall's observations in particular appear to be almost conclusive against it. Thus 

 Hall has shewn ("Graptolites of the Quebec group," p. 28, pi. A, figs. 4, 5, 9) that the 

 cell-partitions may extend' to the axis, and may, nevertheless, leave room for a common 

 canal, as in D. bicornis. The mere fact, therefore, that the cell-partitions reach the 

 axis, as they certainly seem to do in D. folium and in D. cometa, does not justify us 

 in asserting that there is no common canal, in the absence of sections such as those 

 made by Hall. In the case of I), piristis and G. Sagittarius I believe that Mr. Gar- 

 ruthers is in error, and that the cell-partitions do not really reach the axis, at any 

 rate in full-grown specimens. In J), pristis, His. I have observed conclusive 

 evidence of the existence of the common canal as a distinct structure, since the axis, 

 where prolonged beyond the distal extremity of the stipe, is in some specimens 

 bordered by the common canal on both sides, the cellules alone being wanting, either 

 because they have fallen off previously to fossiUzatiou, or because they had not yet 

 been developed. 



