GRAPTOLITES. 3s 
margins, projecting but little beyond the regular cellules, and, becoming 
enlarged, form elongated sacs with swollen extremities, which are finally 
dehiscent; and then, as I suppose, discharging the ovules or germs, are 
gradually absorbed or dissipated. 
Although these sacs are distinctly defined, they have scarcely any 
apparent substance, except along the lateral margins, which are limited 
by a filiform extension resembling the solid axis of a graptolite. There 
are likewise numerous fibres of this kind traversing the sacs; and these 
sometimes remain attached to the original stipe after the other parts are 
separated. In one example, we have conclusive evidence that they are 
connected with the solid axis of the parent stipe. The gradations of 
development in these sacs may be studied in the figures 6-9, plate B. 
In the specimen fig.10 of the same plate the ordinary cellules are removed, 
and the fibres are still seen jomed to the axis, showing the origin of the 
reproductive sacs. In most specimens bearing these sacs, the cellules of 
the stipe are so obscure that the species cannot be determined ; but in 
fig. 9 we find them attached to a well-marked stipe of G. Whitfieldi. 
This mode of reproduction in the graptolites shows much analogy with 
the Hydroidea, and would indicate the sertularians as their nearest 
analogues.* 
Upon the surfaces of the slate where these bodies occur, there are 
numerous graptolitic germs, or young graptolites of extremely minute 
proportions, ranging from those where the first indications of their form 
can be discovered, through successive stages of development till they 
have assumed the determinate characters of the species. 
In several examples, these minute germs have been detected near to 
and in contact with the reproductive sac ; and in one case, there is but a 
hair’s-breadth between one of the fibres of the sac and one of the oblique 
processes at the base of the germ. It cannot be said that we have 
detected the germ actually within the sac; but the numerous young 
individuals lying near them, and upon the surfaces of the same laminz, 
offer very good arguments for supposing that they have been thus derived. 
The earliest defined form which we observe in the’ young graptolites 
*In the recent Sertularia and Campanularia we find ovarian vesicles, in which a 
number of ovules may be enclosed in acommon envelope. These vesicles are developed 
along the side of a stipe or branch, and the ovules are often arranged along a central 
axis, each one communicating with the common axis of the zoophyte. [Jas. J. Lister, 
Philosophical Transactions, 1834, pp. 365-388, pl. ix. Cited also by Dana, “ Structure 
und Classification of Zoophytes.”] 
Prof. McCoy kas stated (British Paleozoic Fossils, p. 4) that he has found near the 
base of the cellules of graptolites, a transverse partition or diaphragm, similar to what 
may be observed in some sertularians, and which he regards as proving similar rela- 
tions; but I have not discovered in any American specimens evidence of such cell- 
diaphragms. 
