On the Calamites of the Coal-measures. 299 



of the second, and the "stylo-cerato-hyal " as a similar secondary 

 segment from the third arch. 



By far the greater part of the cranium fits anterior two-tliirds) is 

 developed by out-growing laminae from the trabeculee, which after 

 a time become fused with the posterior or vertebral part of the skull. 



"When the tadpole is becoming a frog, the hyoid arch undergoes a 

 truly wonderful amount of metamorphosis. 



The upper part, answering to the hyomandibular of the fish (not 

 to the whole of it, but to its upper half), becomes the " incus ;" and 

 a detached segment becomes the " orbiculare," which wedges itself 

 between the incus and the "stapes." The stapes is a "bung" cut 

 out of the " ear-sac." The stylo-cerato-hyal is set free, rises higher 

 and higher, and then articulates with the " opisthotic " region of the 

 ear-sac ; in the toad it coalesces therewith, as in the mammal. The 

 lower part of the hyomandibular coalesces with the back of the pair 

 of the mandibular arch ; and the " symplectic " of the osseous fish 

 appears whilst the tadpole is acquiring its limbs and its lungs, and 

 then melts back again into the arch in front ; it is represented, how- 

 ever, in the bull-frog, but not in the common species, by a distinct 

 bone. 



This very rough and imperfect abstract must serve at present to 

 indicate what has been seen and worked out in this most instructive 

 vertebrate. 



January 26, 1871. — General Sir Edward Sabine, K.C.B., President, 

 in the Chair. 



"On the Organization of the Calamites of the Coal-measures." 

 By W. C. Williamson, F.R.S., Professor of Natural History in 

 Owens College, Manchester. 



Ever since ]\I. Brongniart established his genus Calamodendron, 

 there has prevailed widely a belief that two classes of objects had 

 previously been included under the name of Calamites — the one a 

 thin-walled Equisetaceous plant, the Calamites proper, and the other 

 a hard-wooded Gymnospermous Exogen, known as Calamodendron. 

 This distinction the author rejects as having no existence, the thick- 

 and thin-walled examples having precisely the same typical structure. 

 This consists of a central pith, surrounded by a woody zone, con- 

 taining a circle of woody wedges, and enclosed within a bark of cellular 

 parenchyma. 



The Pith has been solid in the first instance, but very soon be- 

 came fistular, except at the nodes, at each one of which a thin 

 diaphragm of parenchyma extended right across the medullary ca- 

 vity. Eventually the pith underwent a complete absorption, thus 

 enlarging: the fistular interior until it became coextensive with the 

 inner surface of the ligneous zone. 



The Woody Zone. — This commenced in very young states by the 

 formation of a circle of canals stretching longitudinally from one 

 node to the adjoining one. Externally to, but in contact with, these 

 canals a few barred or reticulated vessels were found ; successive ad' 



21* 



