cxxviii BRITISH GRAPTOLITES. 



1896. Ruedemann's preliminary notice on the development of 



Ruedemann, Diplograptus was followed about a year later by a more com- 



" Development and pl e te paper fully illustrated. His previous views are here 



Mode of Growth of . , , ,.„ , , , . „ ., , 



„. , , „ ,, T „ repeated and amplified, but m a tew cases they are somewhat 



Diplograptus, ' N. Y. r : _ _ J 



State G-eol. Annual modified as the result of a further investigation of additional 

 Keport' for 1894. material. 



With regard to the general form of the complete frond of B. pristis and D. 

 Ruedemanni, which consists of many stipes arranged so as to radiate outwards from a 

 central point — the funicle, these stipes are of three different lengths, and are con- 

 nected together to an approximate central form by their virgulas, " or more 

 properly hydrocauli." Ruedemann distinguishes between the virgula proper and 

 the hydrocaulus, " which forms the connecting stem and is a canal containing the 

 virgula of the rhabdosome included in its distal part." 



As to the function of the central disc " which encloses the funicle," it may have 

 served to support the bases of the stipes, it was " certainly a protection to the 

 funicle," and it may have served as a float. 



The basal cyst consists of " two segments resting in the middle on both sides of 

 a subquadrate base, and the test is comparatively thin. The gonangia and rhabdo- 

 somes which proceed from the central disc and funicle, occur below the basal cyst. 

 Ruedemann at first regarded this organ as a " float " or swimming bladder, and 

 believed that the Graptolites floated, on account of (1) the extreme length and 

 thickness of the hydrocaulus in some specimens, which " makes it difficult to 

 imagine how such an extremely thin stem could have supported the long and 

 broad rhabdosome in any other than a suspended position " ; (2) the absence of any 

 evidence of the sessile nature of the colonies ; and (3) their wide distribution, 

 which would be accounted for by their floating habit. This view of their floating 

 habit, however, Ruedemann relinquished in this second paper, on account of the 

 discovery of a large slab in which more than a hundred colonies of D. Ruedemanni 

 are spread out regularly. He considers that the " improbability of such an array 

 of nicely ordered, apparently undisturbed stellate groups having been drifted 

 together is obvious." The hydrocauli and rhabdosomes possess only a very slight 

 flexibility, and therefore it was only where there were no currents in the sea that 

 one could hope to find entire colonies. 



He abandons the floating theory previously held by him, and suggests that the 

 basal cyst was " buried in the detritus " on the floor of the ocean, and served to 

 procure stability for the colony. 



He compares the gonangia or vesicles containing the siculae with certain organs 

 in the Sertularians, and considers that they resemble in all the more important 

 features the Sertularid gonangium, which contains a cylindrical column, the 

 " blastostyle," and he thinks that the possession of these organs and also their 

 structure are arguments for the hydrozoan nature of the Graptolites. 



