THK 



227 



M. Barrande ' has succeeded in tracing out the develop- 

 ment of some species of Trilobites. He finds that the small- 



PIG. 67. Diagram of Dalmanites (after Pictet). A, head ; 1, marginal band ; 8, mar- 

 ginal groove. Internal to the band ; 8, occipital srumnit : J. clabellnm ; 5, great 

 suture ; 6. eyes ; o, fixed genn ; ft, separable gena ; 0, genal angle ; B, thorax ; 7, 

 axis or tergum ; 8, pleuron ; L\ pygidium ; 9, tergal ; 10, plenral portions of the 

 pygidium. 



est, and therefore the youngest, forms are discoidal bodies, 

 without any clear evidence of segmentation. Tin* division 

 into somites takes place by degrees, the number increasing 

 up to the adult condition. It is possible that still younger 

 conditions may have escaped fossilization, but the analogy 

 of Xfrnu&tt suggest that these small disooidal forms really 

 represent the condition in which the Trilobite left the egg. 



Tin: MKKOSTOMATA." The only exist in<r representati 

 this division of tho O-'/x',/--. ,/ is the jrenus Lhmil'i* (tin- l\ 

 Crabs or Horseshoe Crabs), the various species of which are 



.-ifn .In ivntre de Boheme," tome i. Trilobites. 185i. 

 8 H. Woodward, " A M.uio-raph of the Britisl -usUoe* belonging 



to the Order Meroetomata," 1866. 



