and Affinities of Oraptolites. 379 



He describes tliem as " oval, bell-shaped, pyriform, or rounded, 

 provided with a mucro at one extremity, and surrounded en- 

 tirely by a filiform border, resembling in texture the axis of a 

 graptolite." They attain a length of nearly half an inch. 



He has found them not only free, but in many cases attached 

 to the graptolite, not, however, to any constant point ; for some 

 spring " from the common canal, others from the apex of a 

 cellule, and others from the under surface of a cellule, the last 

 two modes being the most frequent." 



The largest of these capsules which he has seen attached 

 did not measure more than a tenth of an inch in diameter ; and 

 Dr. Nicholson believes that at this stage they become detached, 

 and then attain the large size he has observed in the speci- 

 mens found free in the shale ; for he has there found them in 

 all stages of growth, from small rounded bodies, not larger than 

 a pin's head, to bodies nearly half an inch in length. 



Whatever these bodies may be, it is plain that Dr. Nichol- 

 son's account of them is irreconcilable with the supposition 

 that they represent either the gonangia or the gonophores of a 

 hydroid ; for, apart from their supposed development after de- 

 tachment from the colony, their origin from the walls of the 

 denticle is alone decisive on this point. Indeed their con- 

 nexion with the graptolite appears to be purely accidental. 



Hall has called attention to the occurrence, in the same beds 

 which contain the graptolites, of minute free bodies which he 

 regards as the young or " germs " of the graptolites*. In 

 their earliest form they would appear to consist of a little chiti- 

 nous oblong sac traversed longitudinally by a slender chiti- 

 nous filament, which is continued for a little way at both ends 

 beyond the sac, while at one end it is accompanied by two 

 minute lateral spine-like processes. 



This early form has been traced through more advanced 

 stages, in which it has been seen to become more and more 

 elongated, to develope denticles along its length, and finally to 

 attain a form in all essential points identical with that of an 

 adult graptolite. 



Others, slightly diff"ering in shape from those described by 

 Hall, have been also obtained. Indeed these young gra])to- 

 lites (for there is little doubt that Hall is right in so regarding 

 them) are now well known. They are by no means uncom- 

 mon in graptolitic shales, in some examples of which I have 

 seen them abounding in countless multitudes. 



Hall believes that he finds evidence of their having been 

 contained within the so-called reproductive vesicles of the 



* Hall, op. cit. p. .38, pi. B. fio-s. 12-10. 



26* 



