47 



is a very beautiful and perfect specimen ; the central stipe is about 

 two inches long, and it gives off five branches on the right, and 

 four on the left side, all of them clearly and distinctly marked — 

 the fossilized corneous substance being in an excellent state of 

 preservation (Fig. 19). 



Reproduction. 



The mode of reproduction in the Graptolite family is somewhat 

 obscure, but in all probability it was analogous to that of the 

 Sertularian Zoophytes. In the latter, ovarian capsules are devel- 

 oped on the sides of the stipe, resembling the flower buds of a 

 plant. The capsules are generally somewhat larger than the 

 hydrothecae or cellules, and the reproductive Zooids are developed 

 in the interior. These undergo a series of transformations, but 

 remain in permanent connexion with the colony. On the contrary, 

 the ovarian capsules of the Graptolites appear to have become 

 detached in the later stages of their growth, and afterwards to have 

 opened and set free the germs of life within. Professor Nicholson 

 states, in his " British Graptolitidse," that he has in his collection 

 specimens of Graptolites sedgioickii that show minute pear-shaped 

 sacs attached to some of the cellules. Also, that he has other 

 specimens showing sacs or capsules of the same shape, but much 

 enlarged, and in a free state. Those free capsules are found 

 amongst the Graptolites, and are composed of the same horny 

 substance. There is reason to suppose that each of the ovarian 

 capsules, like those of the Sertularians, may have contained quite 

 a host of little germs or " siculas," from which in every species of 

 the Graptolite family, the adult forms have been developed. The 

 sicula has a pointed triangular, or dagger-like shape, without axis 

 or cellules ; at a later stage, a- minute axis appears, either on one 

 side or along the centre, and more advanced forms exhibit two or 

 three small ceUules on one or both sides of the wider end of the 

 sicula, according as the form may be monoprionidian, diprionidian, 

 or tetraprionidian. It is impossible, however, to determine to 

 which species the young form belongs, except in those that have a 

 few of the cellules developed. Almost every species, in the early 



