GRAPTOLITES OF NEW iOUK, PAKT 1 533 



On the other hand, Bid y inograp tus gracilis, a form with 

 extremely long filiform thecae iu the mature stage, possesses in its proximal 

 part shorter, tubular thecae, of the Bryograptus type of thecal structure 

 thus indicating an opposite path of development to that observed in 

 Goniograptus, but which also finds its expression in the cmtogenetic develop- 

 ment of the branch [see fig. 12]. 



As noted before, the directions of the branches in the proximal parts 

 present also an ontogenetic development, indicative of phylogenetic stages 

 passed. Both the direction of the branches and the character of the 

 thecae tend, hence, to supj)ort the same view, viz that the branches, though 

 composed of thecae were connected into physiologic units. 



FiK. 12 Didymograptus K^r^cilis Tornquist. Eularffement of the specimen 

 flglired on plate 14. figure 17 to show more distinctly the sicula and the profirres- 

 sive len^hening of the thecae. Deep kill. x6 



The Avriter has endeavored to demonstrate in the paper on Goniograptus 

 that, not only the branches, but in fact the entire colonies of graptolites 

 were organisms approaching closely to the character of individuals. One 

 finds among the colonies all gradations from loose aggregates of individuals 

 forming colonies to organisms in which, by division of labor, consequent 

 suppression of individuality and the presence of common organs, the colony 

 also morphologically approaches closely to the character of a sole individual, 

 as in the Siphonophora. 



The graptolite rhabdosomes now present, besides the ontogenetic 

 characters of the proximal parts described above, various other features, 

 which are suggestive of the physiologic individuality of the colonies. Some 

 of these are the presence of a common float or pneumatophor, 'observed 

 in several groups, and the geometric arrangement of the branches, which 



