544 HERRI CK E. WILSON 



completeness as an unchanged suture. In the latter case, it is in 

 the Camerata always accompanied by the inserted angle of the 

 apposed radial. In the pentagonal Camerata the reappearance of 

 a suture or group of sutures would unhesitatingly be described as 

 cases of delayed anchylosis. In the hexagonal forms, however, 

 doubts might arise concerning the reappearance of the anterior 

 suture in the three-basaled genera and of the right-anterior suture 

 in the two-basaled genera, since such reappearance would, according 

 to Wachsmuth and Springer, indicate the presence of six basal plates 

 (pp. 492-93). There might also be some question as to whether 

 these reappearances are due to delayed anchylosis or resorption; 

 but until more light can be thrown upon the problem of sutural 

 reappearance by reabsorption of the intrasutural deposit, these 

 abnormalities may well be ascribed to delayed anchylosis. 



3. ANCHYLOSIS AND THE PHYLOGENETIC REAPPEARANCE OF SUTURES 



Anchylosis of the basals, as far as we now know, is an onto- 

 genetically repetitive process, confined to plates and not taking 

 place as a result of cell-group fusion. The basal sutures are always 

 present in ontogenetic development, and constitute phylogene- 

 tically a plane of weakness in the compound plate. This is appar- 

 ently not true of the infrabasals, at least in modern forms, as is 

 shown in the interradial development of two of the infrabasals in 

 the embryo of Antedon. Atavistic reappearance of sutures, by 

 delayed anchylosis, is a possibility, but the cenogenic or phylogenic 

 reappearance of a suture lost through anchylosis is another question. 

 The skeleton of the Echinoderm is deposited in the midst of living 

 tissue and remains under the full control of the ordinary processes 

 of growth, reabsorption, and modification by living tissue. 1 The 

 partial or total absorption of plates, the shifting of sutures, and 

 the reabsorption and modification of the basals in the formation 

 of the centro-dorsal are sufficient evidence of this statement. It 

 seems possible, then, that under the conditions of physiological 

 disturbance (loss of vitality) common in the paracme of develop- 

 ment, 2 failure of anchylosis or reabsorption of the intrasutural 

 deposit might take place, and the sutures reappear as phylogenetic 



1 Ref. 7, p. 350. 2 Ibid., p. 350. 



