GKAI'TOLITES OF NEW YORK. I'AKT 1 533 



On the other hand, D i d y lu o g r a p t ii s gracilis, a form ^vitll 

 extremely long filiform tliecae in the mature stage, possesses in its proximal 

 part shortei", 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 ontogenetic 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 support the same view, viz that the branches, though 

 composed of thecae were connected into physiologic units. 



Flff. 12 D i d y m o g- r a p t u s g- r a c i 1 i s Tcirnquist . Eulargement of the specimen 

 figured on plate U. figure 17 to show more distinctly the sicula and the progres- 

 sive lengthening- 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 ^vhich, l)y division of labor, consequent 

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

 also morphologicall}' approaches closely to the character of a sole individual, 

 as in the Siphonophoia. 



The graptolite rhabdosomes noA\' 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 



