160 M. Edniond Bovdage on the Fusion hetween the 



them later on a veritable phenomenon of anchylosis, bringing 

 about the fusion in question. This is the hypothesis which is 

 adopted by certain autliors * in order to explain how, in the 

 case of Vertebrates, articulations may become anchylosed in 

 consequence of severe and repeated tensions and strains f. 



The violent strains to which the limbs are subjected at the 

 period of the ecdyses must have had an influence so much the 

 more marked and so much the more efficacious in that at this 

 moment the tissues are in an altogether peculiar condition, 

 and since the integumentary layer which will become the 

 new cuticular covering after the shedding of the old envelope 

 is then still soft. The mechanical action occasioned by the 

 strains has easily produced the thickening, the more intense 

 chitinization of the arthrodial membrane, and, in consequence, 

 anchylosis, a condition which, remarkably enough, is pre- 

 cisely the most favourable for securing autotomy in the line 

 of the groove of fusion, which constitutes a locus minoris 

 r€sisi(7itioR. This condition must have been produced as 

 early as the jjrimary epoch in one of the ancestors with 

 tetrameious tarsus of the existing Phasmids (see my 

 communication of June 28, 1897, to the Acadduiie des 

 Sciences) %. The »Stegocephali of this epoch were able to 

 contribute to the perfecting of the disposition ensuring the 

 autofomic process. 



I would add that modifications in the manner of walking 

 must have been produced at different intervals § — modifications 

 which were themselves occasioned by variations in the 

 general foim of the body during the phylogenetic development. 

 They have brought about displacements in the position of the 

 points of support more or less distant from the body, with 

 the object of ensuring the stability of the latter. I think that 

 we must again regard this as a cause of strains and tensions, 

 which have also contributed to the formation of the fusion 

 with which we are dealing. In short, the wa}' in which this 

 special condition has been produced would be explained by 

 the principles of the science which Prof. Giard terms inorpho- 



* See especially Toruier, "DasEntstelien der Geleiikformen," W. Roux's 

 Arcliiv fiir EntwickeluDgsiuechaiiik, 189o. 



t III the articulations of Arthropod limbs the arthrodial membrane is 

 compared to a liyamcnt by II. Willie-Edwards. In the cases of anchylosis 

 among Vertebrates the ligaments of the joints are precisely the parts 

 which become ossified. 



\ Ann. & Mag. Nat. Hist. ser. 6, vol. xx. (1897) pp. 507-510. 



§ Tlies^e mod ificati oils obliging the limbs to be ilexed, to be folded 

 further back, or to extend ihem.selves during locomotion, according to 

 circunislaiucs. 



