GRAPTOLITES OF NEW YORK, PART 1 509 



6 Mode of existence 



The problem of the mode of existence of the graptolites has as a rule 

 been touclied but incidentally by investigators, and the views entertained 

 by various authors regarding its solution differ widely. Moreover, as with 

 but few exceptions, only fragments of the rhabdosomes are known, and these 

 were taken for the whole colonies, these views are mostly based on erroneous 

 conceptions of the rhabdosomes. 



Hall SjQuebec Grapt. p.38,39], though using the term "radicle" for the 

 sicula, considered the Graptoloidea free floating organisms, as appears from 

 the following statement : " For all those species with a single range of cellules, 

 as well as for some with a double range, including Ketiolites, Retiograptus, 

 and Phyllograptus, I conceive that we have already shown a similar plan of 

 development and a uniform mode of existence ; and Ave are constrained to 

 believe that all these forms, in their mature condition, were free floating- 

 bodies in the Silurian seas." In regard to the Dendroidea he " inferred their 

 attachment either to the sea bottom or to foreign bodies," but adds that 

 he has never observed them attached, largely because there do not occur in 

 the graptolite beds any other bodies to which they could be attached ; but 

 neither has any evidence been found of the attachment of the Dictyonemas 

 which in the Niagara, Upper Helderberg and Hamilton groups occur in 

 association Avitli large numbers of other fossils. Richter, Scharenberg and 

 Geiuitz expressed the opinion that the graptolites were attached by tlieir 

 Fuss (sicula), or had this lower extremity plunged into the mud or sand 

 [Geinitz]. Nicholson held that some (as Didymograptus) were attached, and 

 others (as Monograptus and Coenograptus) Avere free. Herrmann assumes 

 " that all graptolites provided with a sicula were not attached bodies," basing 

 his view on the tapering of the sicula into a fine point or nema or its supposed 

 disappearance. He leaves the question open, whether they were inserted into 

 the mud with this free end or kept at small depths " like a Cartesian diver," 

 A\hile, like all other graptologists, he considers the arborescent forms (Den- 

 droidea) as having been attached. 



