FOSSIL HYDKOZOA. 



165 



in which the Graptolites occur, but only doubtfully attached 

 to the fronds of the latter. These we may infer to have 

 been " ovarian vesicles ; " but they differ from the bodies so 

 called in the Sertularians in becoming detached from the 

 parent colony. 



Fig. 56. Supposed " ovarian capsules " or reproductive buds of Graptolites. 



As regards the affinities of the Graptolites, opinions widely differ, 

 though the view now generally adopted by palaeontologists is that they 

 constitute an aberrant and ancient type of the Hydrozoa. In the actual 

 structure of the polypary, as is easily seen by a comparison with the 



B c 



Fig. 57. A, A fragment of Plumularia pentuitula, magnified, showing a single row of hydro- 

 thee* ; B, A fragment of Sertularia fallax, magnified, showing a double row of hydrothecse ; 

 c, Fragment of Sertularia fallax, magnified, showing an ovarian capsule. (After Johnston.) 



subjoined illustration (fig. 57), representing, on an enlarged scale, the 

 shape and arrangement of the hydrothecae among the Sertularida, the 

 Graptolites certainly closely approach the recent Sea-firs, though the 

 latter possess no " solid axis," and the hydrothecse do not overlap, while 

 the polypary is always fixed. In the unquestionable fact, also, that the 



