GRAPTOLITES. on 
Whether the Phyllograptus existed as simple stipes with four ranges of 
cellules, or in a compound arrangement as in Retiograptus, the mode of 
development has been similar: either the germ with its initial point 
developed a single stipe with four ranges of cellules, or the same elements 
first subdivided, and each division gave origin to its stipe through the 
common body. 
In regard to the development of the cellules in the different parts of 
the graptolite, we observe, as a uniform feature, their lesser development 
towards the base of the stipe. In all the monoprionidian forms this char- 
acter is particularly observable ; and in a few species the earlier cellules 
are raised in a scarcely perceptible elevation above the general surface of 
the common envelope. Indeed in a few instances it is impossible to ascer- 
tain satisfactorily whether these earlier prominences are expanded into 
open cellules. As the stipe is extended, they become gradually more and 
more prominent, until towards the middle, or oftener perhaps nearer the 
distal extremity, their greatest degree of development is reached. In some 
species this takes place near the base, and in the more elongated stipes 
there is no sensible increase throughout a great part of their length, and 
the two margins of the stipe are essentially parallel. ‘Towards the distal 
extremity there is a gradual, or often a more abrupt, diminution in the size 
of the cellules, and a few of the last ones are much smaller, until the ter- 
minal cellule is sometimes seen in a partially developed condition between 
the common body and the partition of the preceding cellule. 
The same condition of development in the cellules is true of the diprio- 
nidian forms, as is shown in some degree in G. pristiniformis, plate xiii, 
but more especially in the accompanying figures of G. pristis and G. 
Whitfieldi, the last of which shows the higher cellules diminished, so as to 
contract the width of the stipe above (figs. 30 and 31, p. 86). 
In fetiolites and Retiograptus, the full development of the cellules 
takes place below the middle of the length of the stipe, while they are 
less developed towards either extremity. In some species of fetiolites, 
including one from the Clinton formation, the cellules acquire their greatest 
development near the base, and the margins are essentially parallel for the 
greater part of their length. 
In Phyllograptus, the lesser development of the cellules at the base of 
the stipe is a marked feature. They increase rapidly towards the middle ; 
and their greatest development is sometimes above and sometimes below the 
middle, but im all cases becomes rapidly less towards the apex. 
In Dendrograptus, where we have a stout stem without cellules, the 
branches usually begin at some distance above the base: and in their 
lower part they have scarcely the appearance of being celluliferous ; in 
the middle of their extent the cellules become more distinct, and so far as 
can be observed they are less developed towards the extremities. 
C 
