78 



The Ottaaaa Naturalist. 



[ October 



Hoav does it happen that this trilobite has lost the ends of two 

 of his largest ribs and that a third, which lies betAveen them, has been 

 cut off close to the central part of his body? And what light do Ave 

 receive from the fact that the broken ends of these ribs have started to 

 heal up and show fairly well developed terminations? (See figure 1). 



Fig. 2 Restoration of Sidneyia inexpectans Walcott. Made by grouping 

 together a bodv and two claws found within the limits of the same 

 Middle Cambrian faunule on the slopes of Mt. Field, British Columbia. 

 The two claws are probably both rights or both lefts, one (left in the 

 figure) showing one side, with the "thumb" in place, the other show- 

 ing the reverse side of a claw probably belonging to the same side of 

 the animal, with the "thumb" broken away. The individual portions 

 after Walcott. One-half natural size. 



If we assume that tlie trilobite lost this portion of his anatomy 

 while he was a very small animal, why was he so long about fixing up 

 his lost ribs? Crustacea noAv have the poAver of rebuilding lost parts 

 of their body, and this primitive crab has proven by his ability to heal 



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