HISTORY OF RESEARCH. cxxix 



Ruedemann next discusses briefly the various supposed reproductive organs 

 described by previous authors, and suggests that the " bi-thecse " observed by 

 Holm in Dictyonema should rather be compared with the nematophores of the 

 Plumularians than with gonangia. 



He deals with the development of the sicula at some length, and considers that 

 while there is " conclusive " evidence that numerous siculse left the gonangia, it is 

 also clear that others did not sever their connection with the parent colony, but 

 grew out into new rhabdosomes. 



The development of Diplog. pristis is worked out by him in detail, and his 

 results may be summarised as follows : 



(1) The detached sicula is attached by means of a small round node to a basal 

 appendage. 



(2) The hydrocaulus gradually lengthens and more and more thecas are formed. 



(3) " The node becomes the central disc and funicle. The sicula produces at 

 first one theca, then a second, third, etc." 



(4) The growth of the gonangia (four small capsules) begins with the budding 

 of the first thecae. 



(5) The gonangia mature and open, the siculas, however, remaining connected 

 with the parent colony, the basal cyst, funicle, etc., are all present. 



(6) The siculse grow out to rhabdosomes. 



(7) A second generation of gonangia begin to grow, and the process is 

 continued. 



The " number and length of the rhabdosomes increase with the age of the 

 whole colony." 



Affinities.— As respects the affinities of the Graptolites, he merely states that 

 they should be placed in a distinct class — the Rhabdophora. 



He concludes his paper with a reply to some of the objections raised by Wiman, 

 especially with regard to the terms employed for the various structures. He 

 maintains that the " central discs " of Dichograptus and Diplographis are " geneti- 

 cally identical," but he relinquishes the employment of the term " funicle " for the 

 connecting stem of Diplograptus. He argues also in favour of the " gonangia "- 

 like nature of the capsules described by him. 

 1896. 

 Giirich, In tlie same year, 1896, Gurich published a paper, 



" Bemerkuugen zur "Remarks on the genus Monograptus," in which he discussed 

 Gattung Monographis," the structure, the shape of the thecal aperture, and also the 



' Zeitsch - d - deutsch ' biology of the Monograptidae in general, 

 geol. Gesell.,' vol. xlviii. toJ & r & 



As regards the histology of the Graptolite skeleton, he recognises the four 



structural layers described by Perner, but considers that the appearances are 



capable of a different explanation. He adds many new facts regarding these, and 



considers that the layer "with coigns" is "not the organic structure of a special 



