GRAPTOLITES OF NEW YORK, PART 1 575 



connected by the nematophore-bearing genera of the latter, while they have 

 also important points of connexion with the Rhizopoda." 



The facts which, in Allman's opinion and that of his contemporaries, 

 most obviously opposed themselves to the acceptance of the hydroid affinities 

 of the graptolites were the presence of a solid axis (the virgula) and the 

 unconstricted mode in which the thecal cavity opens into the coenosarcal 

 canal. In regard to the first fact, Rhabdopleura, a living bryozoan, which 

 stands apart from the others by the possession of just such an axis, is 

 pointed out to show that the graptolites, while provided with such axes, 

 might nevertheless have preserved in all respects a typical hydroidal structure. 

 We may emphasize here what, at the time when Allman's discussion 

 ^vas written, was not yet known, namely that only a suborder of the 

 Graptoloidea, the Axonophora, possesses this axis, that the same is 

 hence a late acquirement and not a diagnostic character of the class. 



On account of the absence of the constriction at the basis of the 

 thecae, Allman compares these, not with the hydrothecae which shelter the 

 zooids, but with the calycles Avhich contain the nematophores of the 

 Plumularidae. The nematophores consist of nothing but protoplasm which has 

 the power of emitting pseudopodia. The fact of the presence of dimorphic 

 thecae in the Dendroidea, discovered since, would seem to lend support 

 to the possibility of the suppression of one of these thecal forms in the 

 Graptoloidea. 



More recently however writers have been less positive in their views 

 and have emphasized specially the following facts. (1) That the graptolites 

 not only begin very early in the Upper Cambric but even become extinct 

 in the Middle Devonic, that hence an enormous lapse of time separated 

 the hemera of the graptolites and that of the sertularians and of other 

 Hydrozoa, of which fossil remains are known only from relatively young- 

 formations. (2) It is, as Neumayr \_8tamme des TliierreicJis, p.346] has 

 stated lucidly, a wrong tendency to endeavor to fit all fossil forms into the 

 system of living organisms, a tendency which not only leads to forced and 



