HISTORY OF RESEARCH. cxxxvii 



is the rudder-stem, and the float itself the rudder-fins ; " the fixed Dendroidea 

 have no such organ. 



Freeh does not regard the spine-like appendages to the apertures of the cells, 

 as found in the Glossograptidaa, as of systematic importance, but as protective 

 organs, " perhaps also sensory." 



Freeh divides the Grraptolites into two main groups, differing from each other 

 in the development of the axis, the rudder floats, and common canal, and also in 

 their embryonic stages. 



Order 1 : Axonophora. — This includes Diplograptus, Climacograptus, Dicrano- 

 graptus, Dicellograptus and Monograptus. The sicula is distal in position, and the 

 later polyps insert themselves between the apex of the sicula and the central 

 bladder. The apertures are directed inwards (proximally), a virgula is present, 

 a common canal absent. The mode of life is planktonic, with a passive or active 

 movement. 



Obdee 2 : Axonolipa. — This includes the Dichograptidre and the Dendroidea. 

 The sicula is proximal, and the younger cells grow distally, their apertures being- 

 directed outwards. A common canal for the coenosarc exists in the Dichograptidas, 

 but not in the Dendroidea. " A virgula has not been observed in any of the main 

 types of this order, in spite of numerous microscopic sections." 



The Retiolitidi, according to Freeh, correspond in the structure and arrangement 

 of the hydrothecae, and in the presence of an axis, to Diplograptus ; and Betiolites 

 is a " younger derived form " of that genus. As regards the Dendrograptidi, 

 Freeh accepts Wiman's opinion that they had no axis, and he considers that 

 there are many points of contact between the Dendrograptidi and the Dicho- 

 graptidi. 



B. Embryonal Development of Gra/ptolites. ■ -Freeh gives a summary of 

 Ruedemann's and of Wiman's work, and accepts their conclusions. As regards 

 Ruedemann's work, he seems to think that in addition to the primary hydro- 

 rhabdosomes, there should be " secondary hydro-rhabdosomes," arising direct 

 from the proximal part of the virgula, or from the central plate, and having no 

 siculas, thus producing a colony like that seen in Betiograptus, and he tries to 

 account for the paucity of these non-siculate secondary hydro-rhabdosomes. 



Freeh emphasises strongly his opinion that " an analogy exists between the 

 development of the Axonolipa and the Tabulate Corals," while " the embryonal 

 polyp of Phijlloijraptus has the greatest similarity to the primary calyx of 

 Pleurodictyum." He considers that the terms "Hydrozoa" and " Anthozoa," 

 which are founded on living forms, are in no way applicable to their Palaeozoic 

 ancestors. He places the Graptolithidae as the third member of the following 

 series : 



(a) 1, Archarocyathinia. (b) 2, Acalephas ; 3, Graptolithidae ; 4, Tabulata ; 

 5, Stromatoporoidea. (c) G, Pterocorallia. All except the first and last " take 



t 



