Zoological Position of the Graptolitldge. 59 



the stipe of Graptolites Sedgioickii. These bodies differ from 

 those noticed by Hall in being free in the later stages of their 

 growth, instead of remaining permanently attached. They 

 are oval or bell-shaped, provided with a mucro or spine at one 

 extremity, and surrounded by a strong filiform border, which 

 ultimately ruptures. In many instances these bodies may be 

 seen, when small, to be attached to the cellules of Graptolites 

 Sedgwickii\ and they appear sometimes to spring from the 

 common canal, though this is rare and is perhaps accidental. 



That these bodies are connected in some way with repro- 

 duction appears to me to be beyond doubt. They resemble 

 the " gonophores " of the recent Hydrozoa in being external 

 processes, in some cases permanently attached, in others ulti- 

 mately 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 Graptolites as we now find them in a fossil con- 

 dition, as thought by Hall, but that their contents were the 

 ova in their earliest stages. The ova would probably be libe- 

 rated, on the dehiscence of the capsule, as minute ciliated free- 

 swimming organisms, which subsequently and as a later de- 

 velopment acquired a corneous envelope. With regard to other 

 species of Graptolites, it may be looked upon as probable that 

 the gonophores, if corneous, were attached to the sides of the 

 polypites or to " gonoblastidia," whilst in other species, 

 again, the gonophores were probably without any corneous 

 test; so that the great majority of species will perhaps never 

 be found in conjunction with ovarian capsules, either free or 

 in connexion with the parent stipe. Judging, however, from 

 analogy, there seem to be good grounds for the belief that the 

 reproductive process in all the Graptolitidje was in all essential 

 points identical with that of the Hydi'ozoa. 



Mode of Existence. — As to the mode of existence of 

 the Graptolitidffi, there can be no question that by far the 

 greater number were free-floating or free-swimming organisms. 

 In some species of Bicliograjpsus^ Tetragrafpstis^ and Diplo- 

 grapsus^ there are the remains of a body (the " disk ") which, 

 as I have aleady said, probably acted as a float, and finds its 

 best homologue in the " pneumatocyst " of the Physophorida^. 

 Other genera, as Graptolites^ Phyllograpsus^ Pleurograpsus^ 

 Retiolites^ &c., were very possibly provided with " necto- 

 calyces " or "swimming-bells;" but these, of course, could 



