I 1 8 NEW YORK STATE MUSEUM 



tures by introversion and introtortion with the apparent anxiety to remove 

 the rhabdosome from the base of fixation give one the impression that some, 

 probably creeping enemy had appeared on the seaweeds which threatened 

 the zooids. It may have been such influences that led to the adoption of 

 a holoplanktonic mode of life by the Axonophora. 



b On the phylogenetic relations of the genera of the Graptoloidea Axonophora 

 The abrupt appearance of some of the principal genera of the Grap- 

 toloidea Axonophora in the third Deepkill zone and the slight indications 

 of phyiogenetic relationship between the Axonolipa and Axonophora that 

 have thus far been discovered, have been discussed in Memoir 7 [p. 5 50 ff]. 

 It has been set forth there that the principal new acquisitions of the Axono- 

 phora are the further complication of the colonies into synrhabdosomes and 

 the development of a solid axis (virgula) as support of the nemacaulus 

 after the latter has become incorporated in the rhabdosome as the " axis," 

 giving to the order its name. 



The astogeny of the Axonophora as described by the writer in 1895 

 [see also Mem. 7, p.528] appears to demonstrate by such stages as that 

 reproduced p.528, fig. 4, where a single (primary) rhabdosome is sus- 

 pended from the primary disk, the derivation from forms with simple rhab- 

 dosomes such as the Dichograptidae have. This stage could be readily 

 conceived to be produced by the further continuation of the alternate mode 

 of development of the thecae begun in D i d y m o g rapt u s caduce u s 

 [see ibid. p. 5 50 ff]. From the primary disk or the base of the nemacaulus 

 vesicular bodies filled with siculae grow forth. These have been described 

 by the writer as gonangia and considered as organs of sexual reproduction 

 while Wiman has urged their character as budding individuals. However 

 that may be, it is obviously the production and remaining attached of these 

 siculae which leads to the formation of the new rhabdosomes that combine 

 in the synrhabdosome. It is quite certain that the production of the siculae 

 at the base of the nemacaulus is a feature- inherited from the Axonolipa. 

 While the siculae; of the latter are well known, the place oi their origin has 

 not yet been observed, and since all facts point to a derivation of the 



