JOHN H0PKINSON ON DIPLOGRAPSUS PRISTIS. 207 



evidence brought forward to prove that these problematical bodies 

 have even any connexion with graptolites. The discovery of this 

 specimen throws no light upon this mode of reproduction. It 

 affords, on the other hand, a decided confirmation of Hall's observ- 

 ations ; and as his views have not been generally accepted, the 

 specimen is perhaps of more value than if it were unique. The 

 reproductive sacs figured by Hall are essentially similar to the 

 gonothecas I have here described ; upon the surface of the shale on 

 which they occur there are numerous young graptolites in various 

 stages of growth ; and in one specimen figured, " in connexion 

 with one of the sacs there are two minute germs, one of them lying 

 beneath the sac, and the other just beyond its outer margin and 

 barely separated from its fibres." * 



The presence of these reproductive capsules throws some light 

 upon the affinities of graptolites. It confirms the evidence which 

 their internal structure has already furnished, of their near alliance 

 with the Hydroida. The reproductive organs of the Actinozoa and 

 of the Polyzoa being internal, graptolites cannot, as some think, 

 belong to either of these classes. In the Hydrozoa they are 

 external ; and in some of the Hydroida (the only subclass of the 

 Hydrozoa with which graptolites, having a chitinous polypary, can 

 be compared) there are reproductive capsules essentially similar to 

 those of the graptolite, although in no single instance entirely agree- 

 ing with them. We have no single recent Hydroid with reproduc- 

 tive organs enclosed in chitinous capsules which are destitute of 

 any distinct orifice, are bounded by a marginal fibre, or composed 

 of two membranes united at their edges, and at the same time bud 

 from the periderm without interfering with the continuity of the 

 hydrothecas ; but these appearances are all presented by one or 

 other of the Hydroid zoophytes. In Sertularia, Diphasia, &c, the 

 gonothecee bud from the periderm in the same manner as in the 

 graptolite ; in several genera they are ribbed or thickened at their 

 edges, and in one genus, if not in more, they have no definite 

 distal orifice. In Aglaophenia, I have been kindly informed by 

 the Rev. Thomas Hincks, the gonotheca " is oval in form, with- 

 out orifice, and bounded by a very thin and delicate chitinous 

 wall." 



I need only add that graptolites, having, as is here shown, true 

 gonothecae as well as. hydrothecse, are most nearly and intimately 



* Grapt. Quebec Group, expl. pi. B. fig. 8. 



P 2 



