18 GEOLOGICAL MEMOIRS. 



collection do, on the contrary, confirm the opinion originally ex- 

 pressed : the three orifices correspond with the insertion of the arms ; 

 the three probosces, proceeding from the buccal orifice, are ten- 

 tacle-furrows conducting to the ventral sides of the arms ; and when 

 hereafter the true arms of Hemicosmites shall be found, it will be 

 quoted to the honour of M. von Buch that it was he who first sug- 

 gested their existence. 



As a kind of compensation for the absence of arms, M. von Buch 

 has described a clearly-marked effort of nature to produce them. 

 He discovers them in the interior of the cup, and shows how power- 

 fully they press against and endeavour to break through the en- 

 closing surface, but he finds that their efforts are vain, and that they 

 are merely Molimina brachialia. 



When we consider that according to Miiller's investigations the 

 arms of Crinoidea proceed from the dorsal pole of the cuticular 

 skeleton, and therefore do not proceed from within outwards, this 

 explanation of the organic modification appears to me an incom- 

 plete attempt to explain the case, and therefore inadmissible. All 

 change in organic nature consists of development advancing by meta- 

 morphosis ; but each stage of development includes the whole, the 

 ultimate result with the commencement :— the conclusion of the 

 development is given with the original germ or bud, and on this 

 account, not only the form of organization, but every change un- 

 dergone is only intelligible within the original limits of the organi- 

 zation. 



The manifestations of organic development in all geological 

 epochs can only be considered complete, — in other words, the external 

 conditions at each period, or the aim of creation, can only be under- 

 stood, with reference to perfectly corresponding organic products. 

 The Cystidea must however be considered as incomplete Crinoidea 

 if they had not attained the condition of development permitted and 

 marked out in the germ. 



While however I do not admit these Molimina brachialia, I feel 

 bound to assert distinctly the presence of true arms. All the Cys- 

 tidea were, like the Crinoids, provided with articulated arms ; and 

 this statement is not a mere hypothesis, but is the result of philoso- 

 phical induction from distinct well-grounded facts determined by 

 observation — by the actual presence of the arms in some species, 

 and the presence of tentacle-furrows in the others. 



The Cysddea are also true Crinoids ; either in the young state or 

 throughout life they were attached by an articulated stalk or by a 

 pedicle either to the bottom of the sea or to foreign bodies. They 

 had articulated arms, which, as in Crinoidea, proceeded from the 

 dorsal pole of the cuticular skeleton. Diametrically opposite to the 

 orifice for the pedicle is placed the buccal orifice, and generally 

 close to it is the subcentral anal orifice. The cup differs however 

 from that of the Crinoids by such a predominance of the dorsal 

 side over the ventral, that the latter is often reduced to a minimum, 

 consisting only of the orifice of the mouth, so that the arms gene-- 

 rally appear to be much nearer the mouth than is the case with 



