12 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE 



attention, mainly as the result of palteontological discovery by Cope i, Gaudry^, and 

 Fritsch^; leading to the recognition of the so-called rhachitomous, embolomcrous, and 

 other similar conditions, whicli ln.ve received at the hands of subsequent investigators 

 correspondingly appropriate names. Both on the embryological and the palteonto- 

 logical sides, a considerable amount of evidence has been brought forward for the 

 belief that some such complex type of vertebra as these, i. e. one in which each vertebral 

 seo-ment was made up of a series of paired elements, was the ancestral one, and that 

 the various (;ypes of vertebral structures characteristic of the living groups may have 

 resulted from diverse modification (inequality of growth and suppression) of these. 

 And, in the attempt to substantiate this belief, Manner, in the latest paper ■* on the 

 subject, has sought to show that from the first period of its differentiation in cellular 

 tissue, the individual " sclerotome " of the Lacertilian is a compound structure. Goette, 

 basing his arguments, like Manner, mainly upon the study of the Reptilian backbone, 

 has concluded^ that the vertebrte of the living " digitata " have arisen from the embo- 

 lomcrous type, and he regards the rhachitomous type as " neither primitive nor 

 independent, but transitional."' If, however, the relationships of these are really direct, 

 we would rather transpose the order, since we regard the greater extension of the 

 skeletogenous tissues, and consequent deeper constriction of the notochord, occurring in 

 the embolomcrous type as indicative of advance upon the rhachitomous, as ali-eady 

 pointed out by Gadow ^. He, working on this basis, has simplified our conceptions of 

 tlie fundamental constitution of the diverse forms of vertebral structure represented 

 among the living vertebrata, beyond his predecessors, by the introduction of a 

 systematic terminolosy based on the supposition that all surviving forms of vertebrae 

 are constituted more or less of two pairs of dorsal and two of ventral elements 

 symmetrically disposed, and that ' " the solution of the composition of the vertebral 

 column is given by the metameric repetition " of these, " the origin of which can be 

 traced in fishes." His terms " basi- " and " inter-" " dorsalia," " basi- " and "inter-"' 

 " ventralia," are most welcome ; and the arguments and conclusions drawn by him 

 certainly furnish a possible explanation of some of the great anomalies arising out of 

 the mere study of the adult vertebral column among living forms — as, for example, the 

 intervertebral disposition and independence of the " chevron bones " of the Amniota. 

 and the vertebral disposition and confluence with the vertebral bodies of the " haemal 

 arches" of the Urodela. 



' Cope, E. D. : Americ. Nat. 1878, p. 327 ; Proc. Americ. Philos. Soc. vol. svii. 187S. pp. 5T0-o26 ; Trans. 

 Americ. Philos. Soc. vol. xvi. 1886, p. 243. 



■^ Gaudr}', A.: EnchaineineDts d. Monde anim. Foss. Prim., torn. i. (Paris, 1883), p. 263. 



' Fritsch, A. : Fauna d. Gaskohle d. Permform. Bohmens, Bd. ii. 1889, pp. 14 & 24. Cf. also Baur, G.: 

 Biol. Centralbl. Bd. vi. 1886, pp. 332 & 353. 



' Manner, H. : Zeitschr. vriss. Zool. Bd. Ixvi. 1899, p. 43. 



^ Goette, A. : Zeitschr. wiss. Zool. Bd. l.\ii. ] 897, p. 390. 



'■ Gadow, H. : Phi!. Trans, vol. 187 B. 1896, p. 1. 



' Op. cii. p. 50. 



