STUDY OF THE GRAPTOLITJES. 233 



is most extended in the direction of the common body along the solid 

 axis. This little sac contains the germ of the zoophyte, which, extend- 

 ing itself as the common body in its canal along the axis, gives origin to 

 the budding which developes the successive cellules and the gradual 

 building up of the polypary. 



The earliest condition of development is illustrated in fig. 12 of 

 Plate i* At a farther stage of development we have the form better 

 defined, as in fig. 13, where the germ has assumed the general aspect 

 of G. pristts, the slender lateral processes being rectangular to the axis. 



On the left hand of fig. 8, and at the third reproductive sac below the 

 top, there are two germs visible, close to the sac, where the connection 

 between one of these and the fibre is nearly complete. The same is 

 shown in the enlarged fig. 11. 



In fig. 14, we have the germ of another form, which is unequally 

 developed on two sides. Figure 15 (represented of the natural size) 

 appears to be of the same species, having reached a more definite form. 

 Figure 16 is an oval disc, of which several more or less defined speci- 

 mens have been found among the young Graptolites, but I have not been 

 able to trace it to any known mature form. 



The specimens figs. 17 and 18 appear to be the young of G. Mcornis, 

 or of a similar form. In one the body is narrow, without marks of 

 cellules, and the solid axis is not extended above the common body, 

 having probably been broken off. In the other there is a greater expan- 

 sion of the common body, but no cellules are visible, and the central 

 portion of the substance is more dense, while towards the margin it is 

 extremely thin; the solid axis is extended beyond the stipe, and the 

 lateral oblique processes are quite perfect. This germ, with its axis and 

 common body, had not begun to develop the cell-apertures on its margins, 

 which may be seen at a later period. 



In nearly aU the young Graptolites, there is an extension of the com- 

 mon body along the axis above the incipient cellules. This is observed 

 in the figures referred to and in the young of G. ramosus, shown six 

 times enlarged on Plate ii, fig. 21. 



Although I have found none of the monoprionidian forms with repro- 

 ductive sacs attached, I have nevertheless observed what appear to be 

 the young of some of these species, having an aspect similar to the others, 

 except in carrying the development of the coenosarc upon one side only of 



* All the specimens of germs or young Graptolites are six times enlarged, except figs. 11 and 17. 

 Cab. Nat. 30 



