METAZOA VERMES. 289 



illustration of the fact that only under exceptional condi- 

 tions can traces of soft-bodied animals be preserved. 



Such conditions were realized in Mesozoic times by 

 the peculiar clay of the present lithographic slates of 

 Bavaria, the extreme fineness of which made it possible 

 for an impression to be taken and preserved of even so 

 delicate an animal as a jelly fish. The Palaeozoic forma- 

 tions, however, have no lithographic slates, and the 

 occasional indefinite trails (PI. 722, Nereites cambrensis 

 M'Leay), the filled-up burrows (PI. 723, Planolites vul- 

 garis), and the like, are but uncertain evidences in regard 

 to the ancient fleshy progenitors. 



When, however, the descendants of these fleshy ances- 

 tors became specialized to such a degree as to possess 

 masticating organs in the form of chitinous jaws, then 

 these hard parts would be preserved. The fact that such 

 remains (PI. 724, figs, i, 2, jaws of Eunicites, greatly 

 enlarged 1 ) exist in the lower Palaeozoic rocks proves that 

 worms originated in the early geologic times. Corrobo- 

 rative testimony on this point is given by Dr. Hobb's 

 discovery of worm borings and worm teeth in the pre- 

 Cambrian rocks of eastern Massachusetts. 2 



Though we know little of the Palaeozoic predecessors 

 of our present worms, the Bavarian lithographic slates 

 help us greatly in regard to the Mesozoic ancestors. 

 Remains are preserved with sufficient clearness to enable 

 us to determine many of their characteristics. These 

 worms (PL 725, fig. i. Eunicites avitus Ehl.), had long 

 bodies divided into a large number of segments (more 

 clearly seen in fig. 2, Ctenoscohx procerus) . The greatest 

 breadth of the worm is at the anterior end, and the body 

 tapers towards the posterior extremity which is not pre- 

 served in fig. i, but is seen in fig. 2. On either side of 



1 Most of these jaws do not average more than one twelfth of an 

 inch in length. 



2 See Amer. Geol., XXIII, Feb., 1899, p. 109. 



