HISTORY OF RESEARCH. lix 



forming a constituent part of the "germ," but the solid axis, instead of being 

 shown as a continuation of the apex of the sicula, is figured as continued into, and 

 is confused with, the apertural spine of the sicula. 



In a letter written during this year Nicholson replies to 

 Carruthers' criticism of his " Grapto-gonophores," and lie 

 Greol Mae ""vol iv suggests that possibly the pustuliform elevations at the bases 

 of the cells in Didymog. nitidus and l>. anceps "may he the 

 cicatrices of ovarian capsules." 



A subsequent letter from Carruthers called forth a reply 

 from Nicholson, but no new facts were given by either writer. 



1867. 



Nirliohon, 



1867. 

 Carruthers, 

 Geol. Mao-.,' vol. iv. 



1867. 

 'Nicholson, 



A month later Nicholson published another paper, in which 



he suggested the generic name Pleurograptus for the for in 



On a New Genus of typified by the ( 'ladogra/ptus linearis of Carruthers. Nicholson 



G-raptolites, with Notes re-describes the species, showing how it differs from Dendro- 



on Eeproductive graptus, and from all known genera, in having no ' fnnicle,' 



Bodies," ' Geol. Mag.,' the " primitive parent stem being itself cellnliferons." He 



considers that Gr. gracilis, with its marked ' fnnicle,' is 



unique in its character, and " should form the type of a new genus." 



Nicholson also figures in this paper a stipe " studded with small rounded 

 tubercles," " apparently springing from the common canal on either side," and 

 he suggests that this may be an "instance of ovarian vesicles in their young 

 condition," which may either remain permanently attached, or may possibly 

 become free at a later stage. 



He also figures several more " gonophores " of G. Sedgwiekii, and states that 

 he believes that he has " made out with certainty that these capsules are reproductive 

 in function," while their resemblance to orbicular Brachiopods when compressed 

 is "purely mimetic and illusory." Associated with examples of Gr. Sagittarius the 

 capsules occur in the greatest confusion, but he "failed to detect any organic 

 connection between them and the cells." This, he suggests, may be due to the 

 fact that they were thrown off when extremely minute, attaining their full develop- 

 ment subsequently; or they "were attached to the sides of the polypites, or to 

 ' gonoblastidea,' as in many living Hydrozoa." 



He points out the fact that no ovarian sacs are found among the Graptolites at 

 Hartfell — where there are no forms of Graptolithus (Monograptus) ; but he explains 

 this by suggesting that the sacs belonging to the genera there represented had 

 possibly no corneous envelope, and that therefore they have not been preserved. 

 Some additional young forms or germs are figured by him, differing hut little from 

 those previously described, except as respects their greater size. 



Nicholson strongly upholds in this paper the Hydrozoa! affinities of the 

 Graptolites, on the following grounds: 



