478 NEW YORK STATE MUSEUM 



presence of the solid axis which at that time was still supposed to be present 

 in all graptolites proper. 



The investigation of the proximal parts of the rhabdosomes of Tetra- 

 graptus and Didymograptus by Holm, and that of the stipes of Diplograptus 

 and Monograptus by Wiman, allow a conclusion as to the mode of develop- 

 ment of these portions of the colonies. The latter investigator succeeded 

 also in elucidating the mode of reproduction of thecae in Dictyonema, 

 Dendrograptus and Inocaulis. 



JRiiedemann [1895] obtained a complete growth series of Diplo- 

 graptus foliaceus and was, with the aid of this material, able to trace 

 the development of the whole colony of that species from the sicula onward 

 [p. 5 2 8]. Later, a like series has been secured for a multiramous dichograptid, 

 viz Groniograptus thureaui [p.622 and pi. 6]; and in this memoir 

 the development of Dictyonema flabelliforme is described [p.602 

 and pl.l]. 



The study of the phylogeny of the graptolites, aside from the attempts 

 at mere classification by various authors, was not taken up till the last 

 decade. Wiman derived different groups of Monograptus, each by way of 

 its corresponding Dimorphograptus, from Diplograptus and Climacograptus, 

 thus indicating the polyphyletic origin of that genus ; and Nicliolson and 

 Marr [1895] have outlined the path of development of the Dichograptidae, 

 taking the shape and arrangement of the thecae as characters of prime 

 phylogenetic importance. Their results point also to a polyphyletic origin 

 of the large genera of this family and specially of Tetragraptus and Didymo- 

 graptus. Their work has been largely verified and ably continued by Elles 

 [1898]. 



The mode of existence of the graptolites, finally, has as a rule been 

 touched only incidentally, but the problem has lately been discussed by 

 LapworiJi [^QQWalther 1897]. 



