No. 373-] THE STUDY OF GRAPTOLITES. 7 
contain numerous siculz attached by their apical ends (Fig. 10). 
The writer compared these vesicles with the gonangia of the 
sertularians, considering the sicule as the original chitinous 
Fics. 11-20. — The same: devel t of lony (Ruedemann) 
iy 
coverings of the embryos. (Holm sees in the initial part of 
the siculz the covering of the zooid germ.) The development 
of the colony is as follows : 
1. The sicula is provided with a basal appendage to which 
it is attached by means of a little round node (Fig. 11). 
2. The node becomes a central disk and funicle. The sicula 
produces at first one theca, then a second, a third, etc., as 
demonstrated also by Térnquist and Wiman (Figs. 12, 13). 
3. The budding of the thecæ along the lengthening hydro- 
caulus produces the primary rhabdosomes (Figs. 14, 15). 
4. While the latter is formed, gonangia, usually as four small 
capsules, arise from the central disk. At last the latter mature 
and open. Many, or perhaps all, of the sicula remain con- 
nected to the parent colony (Figs. 16, 17). 
5. These siculz grow out to rhabdosomes (Fig. 18). 
