Carruthers — On Graptolites. 71 



over the surface of the laminae, mere juxtaposition, without a trace- 

 able union, is of little importance. I believe the specimen figured 

 by Mr. Nicholson, which was the only one he observed, is a case of 

 mere juxta-position. If we are to be guided in our interpretation of 

 these organisms by the structure and relation of parts in recent 

 forms, it will be difficult to find an ovarian vesicle attached by a 

 large mouth to the polypidom, or having the relation to two cells 

 which is shown in Plate XVII. Fig. 3 (I.e.), and we do not know any 

 hydrozoon which has " corneous ' gonophores' " that become " free 

 swimming ' zooids.' " Supposing the minute fossils to be ovarian 

 vesicles, we would be inclined to consider the elongated mucro to 

 be the pedicel. The broad end is always very faint, indicating that 

 the wall of the capsule was thinner at this place. Indeed the fossil 

 remarkably resembles the gonophore of Sertularia operculata, L. 

 except in the great difference in size. If it belonged to the grapto- 

 lite, we should expect a similar relation to the supporting organism. 

 In Sertularia the o\T.-sac has a very simple structure. In the allied 

 genus Plumularia the sac is composed of the polype-calls of a branch 

 specially altered for this purpose, as was shown by Edward Forbes. 

 It consequently occupies the position of the branch, but in Sertu- 

 laria the sac rises from the surface of the common canal and does 

 not interfere with the symmetry of the parts. I have never been 

 able to detect in any graptolite the suppression of a cell, far less of 

 a series of them, that would indicate their possessing a vesicle 

 having the structure of those of Plumularia, nor have I seen on the 

 polypidom of the fossil any scars that could have been produced by 

 the fall of the capsule. The organisms that Hall found on a species 

 of Diplograpsus have a very different aspect from those found at 

 Moffat. He believes that the contents of the ovi-sacs were minute 

 graptolites like the parent. He figures a small specimen very near 

 to the mouth of a sac, from which he considers it has just escaped. 

 This also would be anomalous in hydrozoa. In the volume of the 

 Proceedings of the Eoyal Physical Society of Edinburgh, published 

 in 1858, I figured a young specimen of my Diplograpsus tricornis, 

 which seems to be the same species as that subsequently figured 

 by Hall under the name of G. WMtfieldii. I have traced its 

 growth from the youngest condition where the three spines were 

 at the proximal end, and the slender solid axis at the distal, and 

 only a delicate membrane expanded between without indication 

 of cells. As the organism grew the cells appeared, and gradually 

 developed around the free portion of the axis. I have noticed a 

 similar growth in D. pristis, His., and I believe also in D. coineta, 

 Gein., a beautiful species not uncommon in the Moffat shales. It 

 would be an important observation if anything like these younger 

 forms could be detected in the interior of a capsule, but in the 

 hundreds I have examined I have seen no indication of their 

 contents ; and in the innumerable specimens of double graptolites 

 which my hammer has laid open, I have never seen anything like 

 what Hall has figured. 



The oval or rounded bodies which Mr. Nicholson figures are most 



