242 Report of the State Geolog-ist. 



Dr. O. Herrmann,^ in the description of Diohograptus Kjerulfi, 

 Herrm., contends that fronds of Dichograpius with a different 

 number of rhabdosomes (from 5 to 14) do not represent different 

 ages, as it has been thought; on the ground that no difference in 

 the thickness and length of the rhabdosomes is to be detected ; 

 that no younger rhabdosomes are perceptible when they had just 

 sprouted and before they reached the margin of the central disc ; 

 and that young individuals occur with eight, nine and twelve 

 rhabdosomes, just as in full-grown specimens. 



It is certainly not analogous with Diplograpius^ for the colony 

 of Biplograptus does not grow as a whole with a given number of 

 rhabdosomes, but the number of the latter is constantly increasing 

 by the development of new rhabdosomes from siculse. This view is 

 supported by Hall's observation that the number of rhabdosomes 

 is no specific character and that there is apparently no law of 

 branching in forms with many rhabdosomes. 



There was no difference in the mode of growth between the 

 primary and the following rhabdosomes. In both the sicula lies 

 in the oldest part, and both grew, as it were, bacliward to ward the 

 center,' forming new thecae at the basal end. One could compare 

 this mode of growth with that of a leaf, the oldest part of which 

 is the most distant point, while the youngest part, where the 

 leaf is growing, is the base of the blade. 



As long as only the detached rhabdosomes of Diplograptus 

 were known it was natural that the sicular end, where the 

 growth of the rhabdosome begins and which at first was 

 thought to be attached to the ground, was called the " proxi- 

 mal " and the opposite the " distal " end. But where we have a 

 funicle and central disc, i. e., a point of attachment of the rhab- 

 dosome, we must follow, in order to avoid confusion in the nomen- 

 clature, the usage of the authors on modern Hydrozoans and 

 define with Huxley "the attached extremity of the fixed hydro- 

 soma or its equivalent in the free one as the proximal end, the 

 opposite, as the distal end." The sicula-bearing end of the rhab- 

 dosome of Diplograptus^ therefore, is really the " distal" end, as 

 is the point of the leaf. 



Wiman holds that the virgula does not begin to develop its 

 proximal part until the sicula has been taken into the rhab- 



*Dr. O. Herrmann: On the Graptolitic Family Dichograptidce, Lapw., Geological Magazine, 1836, 

 p. 18. 



