HISTORY OF RESEARCH. lx.xi.x 



porisarcal tube in the Hydroids. If this suggestion is correct, then the Graptolites 

 would be " morphologically Plumularidans in which the development of hydro- 

 thecas had been suppressed by the great development of the nematophores," 

 " while on the other hand, the existing Plumularidian " " would present in its 

 nematophores the last traces of the structure of its ancient representative, the 

 Graptolite." 



Reproductive Organs. — All man accepts the " gonosomal " nature of the repro- 

 ductive sacs described by Hall and Hopkinson in Dip to. pristis, but rejects the 

 " ovarian vesicles " of Nicholson, regarding their connection with the Graptolite as 

 probably " purely accidental." Although admitting the probability that the 

 appendages observed by Hall belong to the generative system, he is " unable to 

 satisfy " himself that they are the remains of gonangia ; indeed he thinks that they 

 are not capsules at all but " hollow laminae. " He finds an analogue to these in the 

 leaflets which compose the corbulge in Aglaop) hernia. An explanation of the scarcity 

 of these " corbulas " in the case of the Graptolites is hinted at " in their free if 

 not floating habit," for while no specimen of Sargassum in fructification has been 

 discovered in the Sargasso Sea, the fructification of closely allied species which 

 grow attached to rocks, etc., is not at all uncommon. 



Allman in a subsequent note to this work briefly refers to Richter's views on 

 the structure of Graptolites as given in his paper in 1871. He expresses con- 

 siderable doubt as to the presence of two lamina in the test, and of the develop- 

 ment of the common canal from the " foot," and says that he is " unable to find in 

 Richter's arguments any grounds for accepting the Polyzoal affinities of Grap- 

 tolites," although the strise observed by him in the Graptolites compare well with 

 those in Rhabdopleura. 



1873. 

 Hopkinson, 

 " On some Graptolites Some further facts regarding the occurrence of Graptolites 



from the Upper Arenig in the St. David's district were furnished by Hopkinson in 

 rocks of Ramsay 1873. He gives a list of seven species from the Upper 



Arenig Rocks of Ramsay Island. 



Island, St. David's.. 

 ' G-eol. Mao;.,' vol. x. 



The same year Hopkinson wrote a note "On the Occurrence 



Hopkinson, °^ Numerous Species of Graptolites in the Ludlow Rocks of 



' On the Occurrence of Shropshire," adding very considerably to our knowledge of the 



Numerous Species of fauna of these rocks. Six species of Monograptus and two of 



Graptolites in the Ptilograptus were new forms, viz, M. capula, M. clavicula, .1/. 

 Ludlow Rocks of . , r , . . . . , . _ . , . ., . 



Q1 , . „ incurvus, M. leintwardinensis, M. Salweyi, M. serra (the 



Shropshire, " v 



1 Geol. Mao-.,' vol x . three last alone are now identifiable), Ptilog. elegans, and 

 /'. Nicholsoni. 



1873. 



