230 Reviews. — P>'o/. Nicholsons British Graptolites. 



The next two chapters are devoted to the general and special 

 morphology of graptolites. In order to explain their general 

 t^tructure, three well-known species are selected for description as 

 typical forms of the family, and the various aspects each may pre- 

 sent according to the jnode of preservation, and the view exhibited, 

 whether lateral, dorsal, or ventral, are clearly pointed out. This 

 last aspect, to which our author does not assign a name, is that 

 which gives rise to what are called " scalariform " impressions. 

 The original Graptolithus scalaris of Linnaeus is generally believed 

 to have been founded on an impression of this nature, whence the 

 name. 



The structure of the various organs of which the graptolite is 

 composed is then described in detail, and the modifications they 

 undergo in the different genera are fully explained; and this subject 

 is further pursued in the following chaj)ter, which treats of the 

 " nature and functions of the base." We do not see how the term 

 base is reconcilable with the view held by Prof. Nicholson, and abl}^ 

 advocated in this chapter, that the "radiculate" graptolites were 

 free-swimming organisms. If they were so, we have no right to 

 assume that the proximal end of the polypary M^as invariably lower- 

 most; and even then the term would scarcely be appropriate. 

 "With the " dendroid " graptolites the case is different, for, since the 

 publication of the work under review, the inference that these 

 forms " may have been attached to the sea-bottom or to some objects 

 during their growth," which Hall drew from their " general form, 

 and from their analogy with other bodies," has been confirmed by 

 the discovery of a British specimen with a process of attachment 

 . similar to the hydrorhiza of the recent Sertularian zoophytes. 



The sixth chapter treats of " reproduction and development." 

 Only two specimens with organs undoubtedly forming a portion of 

 the reproductive system are known to have been found. One of 

 these was described and figured by Hall in 1858 ; the other by 

 Hopkinson in 1871. The nature of the peculiar bodies described 

 by Nicholson in 1866 as " grapto-gonophores " has not yet been 

 satisfactorily determined ; and though still advocating the opinion 

 then expressed, the author admits that he has no fresh evidence of 

 their connexion with graptolites to bring forward. If his conclusion 

 that these bodies " possessed in their free condition the power of in- 

 dependent growth " is correct, they bear no real analogy to the 

 gonothecse of the Sertularian zoophytes. To these gonothecfB the 

 persistent capsules found by Hall and Hopkinson on Diplograptus 

 Whitfieldi and D. pristis respectively, bear a most striking re- 

 semblance, and being external processes, show that graptolites are 

 truly Hydrozoa, and not Polyzoa. 



This question is treated of in the succeeding chapter, in which 

 the author, after briefly stating his views on the mode of existence 

 of the radiculate and dendroid graptolites, notices the affinities they 

 present to the Actinozoa, the Hydrozoa, and the Polyzoa. We 

 believe that with the exception of Richter, all recent authorities 

 consider the graptolites to be Hydrozoa ; and AUman has shown the 

 jnconclusiveness of the arguments in favour of the Polyzoan 



