310 THE ORGANISM AS AN HISTORICAL BEING 



strictly homologous, but also that all membrane bones were 

 derived phylogenetically from ossifications present in the 

 skin or in the mucous membrane of the mouth, just as 

 cartilage bones were derived from the cartilaginous skeletons 

 of the primitive Vertebrates. In some cases this manner 

 of derivation could even be observed in ontogeny, as Reichert 

 had seen in the Newt, where certain bones in the roof of the 

 mouth are actually formed by the concrescence of little teeth, 

 (supra, p. 163). Hertwig considered that the following bones 

 were originally formed by coalescence of teeth parasphenoid, 

 vomer, palatine, pterygoid, the tooth-bearing part of the 

 pre-maxillary, the maxillary, the dentary and certain bones 

 of the hyo-mandibular skeleton of Teleosts. All the investing 

 bones (Deckk/toc/icn} of the skull were of common origin, 

 and could be traced back to integumentary skeletal plates, 

 which in the ancestral fish formed a dense carapace. 



These conclusions were accepted by Kolliker himself, 

 who wrote in his Entwickelungsgeschichte (1879) "The 

 distinction between the primary or primordial, and the 

 investing or secondary bones is from the morphological 

 standpoint sharp and definite. The former are ossifications 

 of the (cartilaginous) primordial skeleton, the latter are 

 formed outside this skeleton, and are probably all ossifications 

 of the skin or the mucous membrane" (p. 464). 



Gegenbaur x consistently upheld the phylogenetic deriva- 

 tion of investing bones from dermal ossifications, and even 

 went further and derived substitutionary bones as well from 

 the integument, thus establishing a direct comparison between 

 the skeletal formations of Vertebrates and Invertebrates. 

 Investing bones were actual integumentary ossifications 

 which had gradually sunk beneath the skin to become part 

 of the internal skeleton ; substitutionary bones were produced 

 by cells (osteoblasts) which were ultimately derived from the 

 integument. - 



1 Vergldch. Anat, </. Wirbelthiere^ i., pp. 200-1, 1898. 



-' For a full historical account of work on membrane and cartilage 

 bones (as well as on the theory of the skull) sec E. Gaupp, " Altere und 

 neuere Arbeiten liber den \Virbclthicrschadel," Ergeb. Anat. Enhv., x., 

 1901, and " Die Entwickclung des Kopfskelettes," in liertwiy's Handbuch 

 vergl. cxper. Entivickclttngslehre d. Wirbeltkiere? iii., 2, pp. 573-874, 

 1905. 



