70 W, Carruthers — On the British Graptolites, 



is utterly impossible in several genera {Bichograpsus, Cladograpsus, 

 JD'icranograptus^ etc), and extremely unlikely in all. As all the 

 oceanic Hydrozoa of our present seas are entirely destitute of a hard 

 outer layer, and have an excessively contractile coenosarc, it is '' very 

 possible," indeed ''beyond doubt," that the Silurian seas were dif- 

 ferently constituted to meet the requirements of Dr. Nicholson's hard, 

 chitinous, and non-contractile free-swimming polypary. 



I will refer to only one other point in Dr. Nicholson's paper, — it 

 would afford endless material for a persevering commentator, — and 

 to that because it is one which the author has been diligently inves- 

 tigating for some time, and in which consequently he has attained 

 some proficiency. I refer to his '' Graptogonophores." In 1866 he 

 published his great disco \^ery, first at the British Association and 

 then in the Geological Magazine for November of that year. He 

 found bell-shaped bodies organically attached by their broad ends to 

 " GraptoUthus Sedgwickii.'' These were " gonophores or ovarian vesi- 

 cles." (Geol. Mag. Vol. III. PL XVII. p. 489.) In the February 

 Number of 1867, I suggested in a note on the systematic position of 

 graptolites that if the bodies had anything to do with the graptolite, 

 the specimen as figured by him was turned upside down {loc. cit. 

 Vol. IV. p. 71). By the following June he had discovered that he 

 was wrong ; but, without taking any notice of his error or my cor- 

 rection of it, he gives drawings of the bodies attached by the slender 

 pedicel to different parts of the polypary {he. cit. PL XI. p. 259). In 

 the next Number I pointed out the error of supposing that the 

 ovarian capsules could be borne in the same species on the common 

 coenosarc, as well as developed from the individual polypites {loc. 

 cit. p. 336). At the meeting of the British Association in September 

 last he gave up the origin from the coenosarc, and in the paper just 

 published in the '' Annals" he tries to let himself more quietly down 

 by saying that such an origin " is perhaps accidental ; " but during 

 the progress of his knowledge he nowhere acknowledges being in- 

 debted for corrections. But now he has established his position 

 " beyond doubt." And this is his last account of the bell-shaped 

 bodies : — " They resemble the gonophores of the recent Hydrozoa 

 in being external processes, in some cases permanently attached, in 

 others ultimately detached; the likeness in form is also striking. 

 They differ, however, in possessing a corneous envelope, so that, 

 when detached, they were either simple free-floating organisms, or, 

 if they possessed any independent locomotive power of their own, 

 this must have been obtained by means of cilia or by some soft 

 apparatus which would leave no traces of its existence. It is 

 probable that the capsules did not contain the germs of grapto- 

 lites as we now find them in a fossil condition, as thought by Hall, 

 but that their contents were the ova in their earliest stages. The 

 ova would probably be liberated, on the dehiscence of the capsule, as 



we have quoted from, he tells us that the minute corneous germ he describes is *' the 

 primitive structure of the embryo," in imagination, that is, for he immediately adds 

 " it must, in fact, be considered very probable that these germs, as we see them, 

 are considerably advanced in growth, and that the earliest form of the embryo was 

 devoid of any corneous test." 



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