REPORT OF THE STATE PALEONTOLOGIST 1901 591 



the youngest stages and of the resulting central parts of the 

 later colonies will easily show. 



It is significant that, as in the Siphonophora. the floating 

 habit appears to have been principally instrumental in bringing 

 about the development of other features suggestive of the 

 morphologic individuality of the colony. Some of these are the 

 presence of a common float or pneumatophor, observed in sev- 

 eral groups, and the geometric arrangement of the branches, 

 which becomes progressively more rigid, and which served to 

 maintain the equilibrium and to give to the greatest number of 

 zooids the most advantageous position. 



If the graptolites so closely approached the morphologic value 

 of an individual, it may be expected that, like an individual, the 

 whole colony had its ontogeny and repassed ancestral stages. 

 To these stages, as a glance at the regularly changing features 

 of the growing colonies of Goniograptus will show, may be 

 properly applied the terminology introduced by Hyatt for the 

 ontogenetic stages of an individual. 



The embryonic stage is clearly present in the initial part of 

 the sicula, which, as Wiman has demonstrated, is differ- 

 entiated from the distal part of the sicula by the nature 

 of the periderm, which is thin, pellucid and possesses no growth 

 lines. Holm 1 asserts his belief that this initial, more pointed 

 end of the sicula " corresponds to the original chitinous cover- 

 ing of the free zooid germ or embryo." This initial part holds 

 a position similar to the protoconch of the cephalopod shell. 

 The nepionic or infantile stage is represented by the stages 

 (fig. 1-6) in which the successive dichotomous divisions produce 

 the stems. It begins with the formation of the apertural part of 

 the sicula. The neanic or adolescent stage of the colony begins 

 with the formation of the branches with serial arrangement of 

 thecae and ends, in the Goniograptus material from the 

 Deep kill, with the production of six such branches on each of 

 the four stems. After this, in the ephebic or mature stage, the 

 branches continue to grow out to full length. Distinctive 



^eol. mag. 1895. 2d ser. 32:435. 



