THE GRAPTOLITES. 361 



long the professor will give to the world the full results of 

 his prolonged researches into the history of the group. 

 This monograph must necessarily be confined to an account 

 of the British graptolites, but when that is complete surely 

 Professor Lapworth will treat of those of other countries 

 also. 



The graptolites, at one time referred by some writers to 

 the Hydrozoa, by others to the Polyzoa, are now generally 

 admitted to belong to the former class, though the exact 

 value of the sub-division is not definitely settled, for whereas 

 we find Professor von Zittel in his Paleontology treating of 

 them as a sub-order, Graptolithidse (= Rhabdophora, All- 

 man), divided into the groups Graptolitoidea Lapw. and 

 Retioloidea Lapw., Nicholson and Lydekker {Manual of 

 Paleontology) place them in a sub-class (Graptolitoidea). 

 In these works the general structure of the graptolites is 

 described, though, as will be seen in the sequel, one structure 

 supposed to be absolutely characteristic of all graptolites, 

 namely the virgula, is not really so. Comparatively little 

 has been added to the knowledge of the histology of the 

 graptolitoidea furnished by H. Richter (5), though some of 

 his results have been confirmed by Professor Sollas (6) ; 

 and additional information has been supplied by Professor 

 S. L. Tornquist (7) and Dr. Perner (8). Some of the most 

 important papers published of recent years treat especially 

 of the mode of growth of the proximal portions of the 

 graptolites. The first of these by Tornquist (9) is occupied 

 with a description of sections through several deprionidian 

 graptolites. The author distinguishes the obverse from the 

 reverse aspect of the polypary, and also introduces two 

 terms to distinguish its right and left portions — the " primor- 

 dial " portion, containing the "primordial" series of hydro- 

 thecae, is marked by the possession of the earliest hydro- 

 theca, whilst the other portion is termed the "second" 

 portion and possesses the second series of hydrothecse. 

 When the obverse aspect of the polypary is turned towards 

 the observer the primordial series of hydrothecae is in- 

 variably on the left hand. The sicula sends out what the 

 author terms a " connecting canal ' which opens into a 



