The Era of Invertebrates 



into three sections crosswise. Some trilobites, 

 and especially the later forms, could roll them- 

 selves into a ball, just as can be done by some of 

 the smaller armadillos, or on a much reduced 

 scale by the so-called pill-bugs, or sow-bugs ; in 

 fact, the pill-bug bears a general resemblance 

 to a diminutive trilobite, to which, indeed, it is 

 believed to be related. 



For a long time after the discovery of 

 trilobites it was a moot question whether or 

 not they had legs ; thousands were found lying 

 out flat or rolled up into compact little balls, 

 but never one with any sign of legs. Fi- 

 nally a specimen was found in Canada with a 

 few legs preserved, and some bearing a single 

 leg. Then Mr. Walcott attacked the problem 

 by making scores upon scores of sections 

 through rolled-up specimens of a species of 

 Calymene, found at Trenton Falls, in which 

 legs, if present, should have been protected and 

 preserved. These sections, by showing portions 

 of the legs where they were cut across, made 

 it very evident that numerous legs had been 

 present in the living animals, while by care- 



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